diff --git a/.github/workflows/php.yml b/.github/workflows/php.yml
index 406615b..8ab7a4f 100644
--- a/.github/workflows/php.yml
+++ b/.github/workflows/php.yml
@@ -37,3 +37,6 @@ jobs:
 
     - name: Run SCA
       run: composer run-script phpstan
+      
+    - name: Run CS
+      run: composer run-script fix-cs:dry-run
diff --git a/.gitignore b/.gitignore
index c3fbeb4..0b78b7e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
 vendor/
 composer.lock
 client.php
-/.phpunit.result.cache
-/.idea/
-/.php_cs.cache
+.phpunit.result.cache
+.idea/
+.php_cs.cache
+.php-cs-fixer.cache
diff --git a/CHANGELOG.md b/CHANGELOG.md
index ad42bf2..178b84c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,14 @@
 # Changelog
 
+## v3.0.0 (22. Mar 2022)
+
+Changes:
+- Added full PHP 8 support
+- Removed support for pre PHP 7.4
+- Improved the code style and added SCA
+  - Added type hints
+- Copyright updated
+
 ## v2.1.1 (21. Mar 2022)
 
 Bug Fixes:
diff --git a/composer.json b/composer.json
index 6858dd8..98744d6 100644
--- a/composer.json
+++ b/composer.json
@@ -3,16 +3,20 @@
   "description": "Implementation of the Billbee custom shop API in PHP",
   "type": "library",
   "require": {
-    "php": "5.6.* || ^7.0 || ^8.0",
+    "php": "^7.4 || ^8.0",
     "psr/http-message": "^1.0",
     "jms/serializer": "^1.14.0 || ^3.14.0",
     "ralouphie/getallheaders": "~3.0",
-    "mintware-de/streams": "^1.0",
+    "mintware-de/streams": "^2.0.0",
     "ext-json": "*"
   },
   "require-dev": {
-    "phpunit/phpunit": "^5.7 || ^7.0 || ^8.0 || ^9.0",
-    "friendsofphp/php-cs-fixer": "^2.15"
+    "phpunit/phpunit": "^7.0 || ^8.0 || ^9.0",
+    "friendsofphp/php-cs-fixer": "^v3.8.0",
+    "phpstan/phpstan": "^1.4"
+  },
+  "suggest": {
+    "ext-xdebug": "*"
   },
   "license": "MIT",
   "authors": [
@@ -32,6 +36,16 @@
     "fix-cs": [
       "./vendor/bin/php-cs-fixer fix ./src/ --using-cache=no --rules=@PSR2",
       "./vendor/bin/php-cs-fixer fix ./tests/ --using-cache=no --rules=@PSR2"
+    ],
+    "fix-cs:dry-run": [
+      "./vendor/bin/php-cs-fixer fix ./src/ --using-cache=no --rules=@PSR2 --dry-run",
+      "./vendor/bin/php-cs-fixer fix ./tests/ --using-cache=no --rules=@PSR2 --dry-run"
+    ],
+    "phpstan": [
+      "./vendor/bin/phpstan"
+    ],
+    "test": [
+      "./vendor/bin/phpunit"
     ]
   },
   "archive": {
diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 0000000..a4c8812
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,5 @@
+parameters:
+	level: max
+	paths:
+		- src
+		- tests
diff --git a/phpunit.xml b/phpunit.xml
index 28f7a6a..d45b2c6 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -2,7 +2,7 @@
 <!--
   ~ This file is part of the Billbee Custom Shop API package.
   ~
-  ~ Copyright 2019 by Billbee GmbH
+  ~ Copyright 2019-2022 by Billbee GmbH
   ~
   ~ For the full copyright and license information, please read the LICENSE
   ~ file that was distributed with this source code.
@@ -17,7 +17,7 @@
   </coverage>
   <testsuites>
     <testsuite name="UnitTests">
-      <directory suffix="Test.php">./tests/</directory>
+      <directory>./tests/</directory>
     </testsuite>
   </testsuites>
 </phpunit>
diff --git a/src/Exception/NotImplementedException.php b/src/Exception/NotImplementedException.php
index 7097eb1..2f45cca 100644
--- a/src/Exception/NotImplementedException.php
+++ b/src/Exception/NotImplementedException.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -13,10 +13,11 @@
 namespace Billbee\CustomShopApi\Exception;
 
 use Exception;
+use Throwable;
 
 class NotImplementedException extends Exception
 {
-    public function __construct($code = 0, $previous = null)
+    public function __construct(int $code = 0, Throwable $previous = null)
     {
         parent::__construct("Diese Aktion ist nicht implementiert", $code, $previous);
     }
diff --git a/src/Exception/OrderNotFoundException.php b/src/Exception/OrderNotFoundException.php
index 027d112..26473ac 100644
--- a/src/Exception/OrderNotFoundException.php
+++ b/src/Exception/OrderNotFoundException.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
diff --git a/src/Exception/ProductNotFoundException.php b/src/Exception/ProductNotFoundException.php
index c0675c1..fbfe1c6 100644
--- a/src/Exception/ProductNotFoundException.php
+++ b/src/Exception/ProductNotFoundException.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
diff --git a/src/Http/Message.php b/src/Http/Message.php
index 1549418..46e63d8 100644
--- a/src/Http/Message.php
+++ b/src/Http/Message.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -12,28 +12,40 @@
 
 namespace Billbee\CustomShopApi\Http;
 
+use MintWare\Streams\MemoryStream;
+use Psr\Http\Message\MessageInterface;
 use Psr\Http\Message\StreamInterface;
 
-abstract class Message
+/**
+ * @template T
+ */
+abstract class Message implements MessageInterface
 {
-    protected $protocolVersion = "1.1";
+    protected string $protocolVersion = "1.1";
 
-    /** @var string[][] */
-    protected $headers = [];
+    /** @var array<array<string>> */
+    protected array $headers = [];
 
     /** @var StreamInterface */
-    protected $body;
+    protected StreamInterface $body;
 
+    public function __construct()
+    {
+        $this->body = new MemoryStream(null);
+    }
 
-    /** @inheritDoc */
-    public function getProtocolVersion()
+    public function getProtocolVersion(): string
     {
         return $this->protocolVersion;
     }
 
-    /** @inheritDoc */
+    /**
+     * @inheritDoc
+     * @phpstan-return T
+     */
     public function withProtocolVersion($version)
     {
+        /** @var T $request */
         $request = clone $this;
         $request->protocolVersion = $version;
 
@@ -41,7 +53,7 @@ public function withProtocolVersion($version)
     }
 
     /** @inheritDoc */
-    public function getHeaders()
+    public function getHeaders(): array
     {
         return $this->headers;
     }
@@ -72,9 +84,13 @@ public function getHeaderLine($name)
         return $line;
     }
 
-    /** @inheritDoc */
+    /**
+     * @inheritDoc
+     * @phpstan-return T
+     */
     public function withHeader($name, $value)
     {
+        /** @var T $request */
         $request = clone $this;
 
         $request->headers[$name] = is_array($value) ? $value : [$value];
@@ -82,15 +98,22 @@ public function withHeader($name, $value)
         return $request;
     }
 
-    /** @inheritDoc */
+    /**
+     * @inheritDoc
+     * @phpstan-return T
+     */
     public function withAddedHeader($name, $value)
     {
         return $this->withHeader($name, $value);
     }
 
-    /** @inheritDoc */
+    /**
+     * @inheritDoc
+     * @phpstan-return T
+     */
     public function withoutHeader($name)
     {
+        /** @var T $request */
         $request = clone $this;
 
         if ($request->hasHeader($name)) {
@@ -100,15 +123,18 @@ public function withoutHeader($name)
         return $request;
     }
 
-    /** @inheritDoc */
-    public function getBody()
+    public function getBody(): ?StreamInterface
     {
         return $this->body;
     }
 
-    /** @inheritDoc */
+    /**
+     * @inheritDoc
+     * @phpstan-return T
+     */
     public function withBody(StreamInterface $body)
     {
+        /** @var T $request */
         $request = clone $this;
 
         $request->body = $body;
diff --git a/src/Http/Request.php b/src/Http/Request.php
index 855b6cb..f00ff39 100644
--- a/src/Http/Request.php
+++ b/src/Http/Request.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -17,19 +17,18 @@
 use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\UriInterface;
 
-/** @inheritDoc */
+/**
+ * @extends Message<Request>
+ */
 class Request extends Message implements RequestInterface
 {
-    /** @var string */
-    private $requestTarget;
+    private string $requestTarget = '';
 
-    /** @var string */
-    private $method;
+    private string $method = 'GET';
 
-    /** @var UriInterface */
-    private $uri;
+    private UriInterface $uri;
 
-    public static function createFromGlobals()
+    public static function createFromGlobals(): Request
     {
         $request = new Request();
 
@@ -62,12 +61,15 @@ public static function createFromGlobals()
     }
 
     /** @inheritDoc */
-    public function getRequestTarget()
+    public function getRequestTarget(): string
     {
         return $this->requestTarget;
     }
 
-    /** @inheritDoc */
+    /**
+     * @inheritDoc
+     * @param string $requestTarget
+     */
     public function withRequestTarget($requestTarget)
     {
         $request = clone $this;
@@ -78,7 +80,7 @@ public function withRequestTarget($requestTarget)
     }
 
     /** @inheritDoc */
-    public function getMethod()
+    public function getMethod(): string
     {
         return $this->method;
     }
@@ -94,7 +96,7 @@ public function withMethod($method)
     }
 
     /** @inheritDoc */
-    public function getUri()
+    public function getUri(): UriInterface
     {
         return $this->uri;
     }
diff --git a/src/Http/RequestHandlerInterface.php b/src/Http/RequestHandlerInterface.php
index 18ae1fe..de9d7fb 100644
--- a/src/Http/RequestHandlerInterface.php
+++ b/src/Http/RequestHandlerInterface.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -16,7 +16,13 @@
 
 interface RequestHandlerInterface
 {
-    public function handle(RequestInterface $request, $queryArgs = []);
+    /**
+     * @param array<string, string> $queryArgs
+     */
+    public function handle(RequestInterface $request, array $queryArgs = []): Response;
 
-    public function canHandle(RequestInterface $request, $queryArgs = []);
+    /**
+     * @param array<string, string> $queryArgs
+     */
+    public function canHandle(RequestInterface $request, array $queryArgs = []): bool;
 }
diff --git a/src/Http/RequestHandlerPool.php b/src/Http/RequestHandlerPool.php
index 6b3f647..d3028a7 100644
--- a/src/Http/RequestHandlerPool.php
+++ b/src/Http/RequestHandlerPool.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -27,20 +27,18 @@
 
 class RequestHandlerPool
 {
-    /** @var AuthenticatorInterface */
-    private $authenticator;
+    private ?AuthenticatorInterface $authenticator;
 
     /** @var RequestHandlerInterface[] */
-    private $requestHandlers = [];
+    private array $requestHandlers = [];
 
     /**
      * RequestHandlerPool constructor.
-     * @param AuthenticatorInterface $authenticator
      * @param RepositoryInterface[] $repositories The repositories
      */
     public function __construct(
-        $authenticator,
-        $repositories = []
+        ?AuthenticatorInterface $authenticator,
+        array $repositories = []
     ) {
         AnnotationRegistry::registerLoader('class_exists');
 
@@ -65,7 +63,7 @@ public function __construct(
         }
     }
 
-    public function handle(RequestInterface $request)
+    public function handle(RequestInterface $request): Response
     {
         parse_str($request->getUri()->getQuery(), $arguments);
 
@@ -86,10 +84,7 @@ public function handle(RequestInterface $request)
         return Response::badRequest('Diese Aktion ist nicht implementiert.');
     }
 
-    /**
-     * @return AuthenticatorInterface
-     */
-    public function getAuthenticator()
+    public function getAuthenticator(): ?AuthenticatorInterface
     {
         return $this->authenticator;
     }
@@ -97,7 +92,7 @@ public function getAuthenticator()
     /**
      * @return RequestHandlerInterface[]
      */
-    public function getRequestHandlers()
+    public function getRequestHandlers(): array
     {
         return $this->requestHandlers;
     }
diff --git a/src/Http/Response.php b/src/Http/Response.php
index 270fc85..6a876ad 100644
--- a/src/Http/Response.php
+++ b/src/Http/Response.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -12,6 +12,7 @@
 
 namespace Billbee\CustomShopApi\Http;
 
+use DateTimeInterface;
 use JMS\Serializer\Handler\DateHandler;
 use JMS\Serializer\Handler\HandlerRegistryInterface;
 use JMS\Serializer\SerializerBuilder;
@@ -19,22 +20,30 @@
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\StreamInterface;
 
-/** @inheritDoc */
+/**
+ * @extends Message<Response>
+ */
 class Response extends Message implements ResponseInterface
 {
-    /** @var int */
-    protected $statusCode = 200;
+    protected int $statusCode = 200;
 
-    /** @var string */
-    protected $reasonPhrase;
+    protected string $reasonPhrase = 'OK';
 
+    /**
+     * @param StreamInterface|string|null $body
+     * @param int $statusCode
+     * @param string $reasonPhrase
+     * @param array<array<string>> $headers
+     * @param string $protocolVersion
+     */
     public function __construct(
         $body = null,
-        $statusCode = 200,
-        $reasonPhrase = 'OK',
-        $headers = [],
-        $protocolVersion = '1.1'
+        int $statusCode = 200,
+        string $reasonPhrase = 'OK',
+        array $headers = [],
+        string $protocolVersion = '1.1'
     ) {
+        parent::__construct();
         if ($body instanceof StreamInterface) {
             $this->body = $body;
         } elseif (is_string($body)) {
@@ -46,24 +55,31 @@ public function __construct(
         $this->protocolVersion = $protocolVersion;
     }
 
+    /**
+     * @param mixed $data
+     * @param int $statusCode
+     * @param string $reasonPhrase
+     * @param array<array<string>> $headers
+     * @param string $protocolVersion
+     * @return Response
+     */
     public static function json(
         $data = null,
-        $statusCode = 200,
-        $reasonPhrase = 'OK',
-        $headers = [],
-        $protocolVersion = '1.1'
-    ) {
+        int $statusCode = 200,
+        string $reasonPhrase = 'OK',
+        array $headers = [],
+        string $protocolVersion = '1.1'
+    ): Response {
         $builder = SerializerBuilder::create();
 
         if (class_exists('\JMS\Serializer\Visitor\Factory\JsonSerializationVisitorFactory')) {
             $factory = new \JMS\Serializer\Visitor\Factory\JsonSerializationVisitorFactory();
             $factory->setOptions(0);
             $builder = $builder->setSerializationVisitor('json', $factory);
-
         }
         $serializer = $builder
             ->configureHandlers(function (HandlerRegistryInterface $handlerRegistry) {
-                $handlerRegistry->registerSubscribingHandler(new DateHandler(\DateTime::ISO8601));
+                $handlerRegistry->registerSubscribingHandler(new DateHandler(DateTimeInterface::ISO8601));
             })
             ->build();
         $json = $serializer->serialize($data, 'json');
@@ -71,43 +87,78 @@ public static function json(
         return new Response($json, $statusCode, $reasonPhrase, $headers, $protocolVersion);
     }
 
+    /**
+     * @param StreamInterface|string|null $body
+     * @param array<array<string>> $headers
+     * @param string $protocolVersion
+     * @return Response
+     */
     public static function notFound(
         $body = null,
-        $headers = [],
-        $protocolVersion = '1.1'
-    ) {
+        array $headers = [],
+        string $protocolVersion = '1.1'
+    ): Response {
         return new Response($body, 404, 'Not Found', $headers, $protocolVersion);
     }
 
+    /**
+     * @param StreamInterface|string|null $body
+     * @param array<array<string>> $headers
+     * @param string $protocolVersion
+     * @return Response
+     */
     public static function unauthorized(
         $body = null,
-        $headers = [],
-        $protocolVersion = '1.1'
-    ) {
+        array $headers = [],
+        string $protocolVersion = '1.1'
+    ): Response {
         return new Response($body, 401, 'Unauthorized', $headers, $protocolVersion);
     }
 
+    /**
+     * @param StreamInterface|string|null $body
+     * @param array<array<string>> $headers
+     * @param string $protocolVersion
+     * @return Response
+     */
     public static function forbidden(
         $body = null,
-        $headers = [],
-        $protocolVersion = '1.1'
-    ) {
+        array $headers = [],
+        string $protocolVersion = '1.1'
+    ): Response {
         return new Response($body, 403, 'Forbidden', $headers, $protocolVersion);
     }
 
+    /**
+     * @param StreamInterface|string|null $body
+     * @param array<array<string>> $headers
+     * @param string $protocolVersion
+     * @return Response
+     */
     public static function badRequest(
         $body = null,
-        $headers = [],
-        $protocolVersion = '1.1'
-    ) {
+        array $headers = [],
+        string $protocolVersion = '1.1'
+    ): Response {
         return new Response($body, 400, 'Bad Request', $headers, $protocolVersion);
     }
 
+    public static function notImplemented(): Response
+    {
+        return Response::badRequest('Diese Aktion ist nicht implementiert.');
+    }
+
+    /**
+     * @param StreamInterface|string|null $body
+     * @param array<array<string>> $headers
+     * @param string $protocolVersion
+     * @return Response
+     */
     public static function internalServerError(
         $body = null,
-        $headers = [],
-        $protocolVersion = '1.1'
-    ) {
+        array $headers = [],
+        string $protocolVersion = '1.1'
+    ): Response {
         return new Response($body, 500, 'Internal Server Error', $headers, $protocolVersion);
     }
 
@@ -115,7 +166,7 @@ public static function internalServerError(
      * Sends the response to the client
      * @param bool $clearBufferBeforeSend Only for testing purposes
      */
-    public function send($clearBufferBeforeSend = true)
+    public function send(bool $clearBufferBeforeSend = true): void
     {
         while ($clearBufferBeforeSend && ob_get_level() > 0) {
             ob_end_clean();
@@ -123,7 +174,7 @@ public function send($clearBufferBeforeSend = true)
         http_response_code($this->statusCode);
 
         if (!$this->hasHeader('content-length')) {
-            $this->headers['content-length'] = strlen($this->body);
+            $this->headers['content-length'] = [(string)strlen($this->body)];
         }
 
         foreach ($this->headers as $header => $val) {
@@ -134,7 +185,7 @@ public function send($clearBufferBeforeSend = true)
     }
 
     /** @inheritDoc */
-    public function getStatusCode()
+    public function getStatusCode(): int
     {
         return $this->statusCode;
     }
@@ -150,7 +201,7 @@ public function withStatus($code, $reasonPhrase = '')
     }
 
     /** @inheritDoc */
-    public function getReasonPhrase()
+    public function getReasonPhrase(): string
     {
         return $this->reasonPhrase;
     }
diff --git a/src/Http/Uri.php b/src/Http/Uri.php
index 556cf83..4471146 100644
--- a/src/Http/Uri.php
+++ b/src/Http/Uri.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -14,41 +14,38 @@
 
 use Psr\Http\Message\UriInterface;
 
-/** @inheritDoc */
 class Uri implements UriInterface
 {
-    /** @var string */
-    protected $uri;
-
-    protected $scheme;
-    protected $authority;
-    protected $userInfo;
-    protected $host;
-    protected $port;
-    protected $path;
-    protected $query;
-    protected $fragment;
-
-    /** @inheritDoc */
-    public function __construct($url)
-    {
-        $this->uri = parse_url($url);
-        $this->scheme = isset($this->uri['scheme']) ? $this->uri['scheme'] : null;
-        $this->host = isset($this->uri['host']) ? $this->uri['host'] : null;
-        $this->port = isset($this->uri['port']) ? $this->uri['port'] : null;
-        $this->path = isset($this->uri['path']) ? $this->uri['path'] : null;
-        $this->query = isset($this->uri['query']) ? $this->uri['query'] : null;
-        $this->fragment = isset($this->uri['fragment']) ? $this->uri['fragment'] : null;
+    /** @var array<int|string, bool|int|string> */
+    protected array $uri;
+    protected string $scheme = '';
+    protected string $authority = '';
+    protected string $userInfo = '';
+    protected string $host = '';
+    protected ?int $port = null;
+    protected string $path = '';
+    protected string $query = '';
+    protected string $fragment = '';
+
+    public function __construct(string $url)
+    {
+        $this->uri = (array)parse_url($url);
+        $this->scheme = $this->uri['scheme'] ?? '';
+        $this->host = $this->uri['host'] ?? '';
+        $this->port = $this->uri['port'] ?? null;
+        $this->path = $this->uri['path'] ?? '';
+        $this->query = $this->uri['query'] ?? '';
+        $this->fragment = $this->uri['fragment'] ?? '';
 
 
         $this->userInfo = implode(':', array_filter([
-            isset($this->uri['user']) ? $this->uri['user'] : '',
-            isset($this->uri['pass']) ? $this->uri['pass'] : ''
+            $this->uri['user'] ?? '',
+            $this->uri['pass'] ?? ''
         ]));
 
         $this->authority = !empty(trim($this->userInfo)) ? $this->userInfo . '@' : '';
         $this->authority .= $this->host;
-        $this->authority .= !empty(trim($this->port)) && $this->port != 80 ? ':' . $this->port : '';
+        $this->authority .= $this->port != null && !empty(trim((string)$this->port)) && $this->port != 80 ? ':' . $this->port : '';
     }
 
 
@@ -59,13 +56,13 @@ public function getScheme()
     }
 
     /** @inheritDoc */
-    public function getAuthority()
+    public function getAuthority(): string
     {
         return $this->authority;
     }
 
     /** @inheritDoc */
-    public function getUserInfo()
+    public function getUserInfo(): string
     {
         return $this->userInfo;
     }
diff --git a/src/Model/Address.php b/src/Model/Address.php
index 27e58e4..4d76a5e 100644
--- a/src/Model/Address.php
+++ b/src/Model/Address.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -20,237 +20,167 @@ class Address
      * @Serializer\SerializedName("firstname")
      * @Serializer\Type("string")
      */
-    public $firstName;
+    public ?string $firstName = null;
 
     /**
      * @Serializer\SerializedName("lastname")
      * @Serializer\Type("string")
      */
-    public $lastName;
+    public ?string $lastName = null;
 
     /**
      * @Serializer\SerializedName("street")
      * @Serializer\Type("string")
      */
-    public $street;
+    public ?string $street = null;
 
     /**
      * @Serializer\SerializedName("housenumber")
      * @Serializer\Type("string")
      */
-    public $houseNumber;
+    public ?string $houseNumber = null;
 
     /**
      * @Serializer\SerializedName("address2")
      * @Serializer\Type("string")
      */
-    public $address2;
+    public ?string $address2 = null;
 
     /**
      * @Serializer\SerializedName("postcode")
      * @Serializer\Type("string")
      */
-    public $postcode;
+    public ?string $postcode = null;
 
     /**
      * @Serializer\SerializedName("city")
      * @Serializer\Type("string")
      */
-    public $city;
+    public ?string $city = null;
 
     /**
      * @Serializer\SerializedName("country_code")
      * @Serializer\Type("string")
      */
-    public $countryCode;
+    public ?string $countryCode = null;
 
     /**
      * @Serializer\SerializedName("company")
      * @Serializer\Type("string")
      */
-    public $company;
+    public ?string $company = null;
 
     /**
      * @Serializer\SerializedName("state")
      * @Serializer\Type("string")
      */
-    public $state;
+    public ?string $state = null;
 
-    /**
-     * @return mixed
-     */
-    public function getFirstName()
+    public function getFirstName(): ?string
     {
         return $this->firstName;
     }
 
-    /**
-     * @param mixed $firstName
-     * @return Address
-     */
-    public function setFirstName($firstName)
+    public function setFirstName(?string $firstName): Address
     {
         $this->firstName = $firstName;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getLastName()
+    public function getLastName(): ?string
     {
         return $this->lastName;
     }
 
-    /**
-     * @param mixed $lastName
-     * @return Address
-     */
-    public function setLastName($lastName)
+    public function setLastName(?string $lastName): Address
     {
         $this->lastName = $lastName;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getStreet()
+    public function getStreet(): ?string
     {
         return $this->street;
     }
 
-    /**
-     * @param mixed $street
-     * @return Address
-     */
-    public function setStreet($street)
+    public function setStreet(?string $street): Address
     {
         $this->street = $street;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getHouseNumber()
+    public function getHouseNumber(): ?string
     {
         return $this->houseNumber;
     }
 
-    /**
-     * @param mixed $houseNumber
-     * @return Address
-     */
-    public function setHouseNumber($houseNumber)
+    public function setHouseNumber(?string $houseNumber): Address
     {
         $this->houseNumber = $houseNumber;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getAddress2()
+    public function getAddress2(): ?string
     {
         return $this->address2;
     }
 
-    /**
-     * @param mixed $address2
-     * @return Address
-     */
-    public function setAddress2($address2)
+    public function setAddress2(?string $address2): Address
     {
         $this->address2 = $address2;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getPostcode()
+    public function getPostcode(): ?string
     {
         return $this->postcode;
     }
 
-    /**
-     * @param mixed $postcode
-     * @return Address
-     */
-    public function setPostcode($postcode)
+    public function setPostcode(?string $postcode): Address
     {
         $this->postcode = $postcode;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getCity()
+    public function getCity(): ?string
     {
         return $this->city;
     }
 
-    /**
-     * @param mixed $city
-     * @return Address
-     */
-    public function setCity($city)
+    public function setCity(?string $city): Address
     {
         $this->city = $city;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getCountryCode()
+    public function getCountryCode(): ?string
     {
         return $this->countryCode;
     }
 
-    /**
-     * @param mixed $countryCode
-     * @return Address
-     */
-    public function setCountryCode($countryCode)
+    public function setCountryCode(?string $countryCode): Address
     {
         $this->countryCode = $countryCode;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getCompany()
+    public function getCompany(): ?string
     {
         return $this->company;
     }
 
-    /**
-     * @param mixed $company
-     * @return Address
-     */
-    public function setCompany($company)
+    public function setCompany(?string $company): Address
     {
         $this->company = $company;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getState()
+    public function getState(): ?string
     {
         return $this->state;
     }
 
-    /**
-     * @param mixed $state
-     * @return Address
-     */
-    public function setState($state)
+    public function setState(?string $state): Address
     {
         $this->state = $state;
         return $this;
diff --git a/src/Model/Order.php b/src/Model/Order.php
index 6a30fbe..18cdb0a 100644
--- a/src/Model/Order.php
+++ b/src/Model/Order.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -12,531 +12,379 @@
 
 namespace Billbee\CustomShopApi\Model;
 
-use DateTime;
+use DateTimeInterface;
 use JMS\Serializer\Annotation as Serializer;
 
 class Order
 {
     /**
-     * @var string
      * @Serializer\SerializedName("order_id")
      * @Serializer\Type("string")
      */
-    public $orderId;
+    public ?string $orderId = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("order_number")
      * @Serializer\Type("string")
      */
-    public $orderNumber;
+    public ?string $orderNumber = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("currency_code")
      * @Serializer\Type("string")
      */
-    public $currencyCode;
+    public ?string $currencyCode = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("delivery_source_country_code")
      * @Serializer\Type("string")
      */
-    public $deliverySourceCountryCode;
+    public ?string $deliverySourceCountryCode = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("nick_name")
      * @Serializer\Type("string")
      */
-    public $nickName;
+    public ?string $nickName = null;
 
     /**
-     * @var float
      * @Serializer\SerializedName("ship_cost")
      * @Serializer\Type("float")
      */
-    public $shipCost;
+    public ?float $shipCost = null;
 
     /**
-     * @var Address
      * @Serializer\SerializedName("invoice_address")
      * @Serializer\Type("Billbee\CustomShopApi\Model\Address")
      */
-    public $invoiceAddress;
+    public ?Address $invoiceAddress = null;
 
     /**
-     * @var Address
      * @Serializer\SerializedName("delivery_address")
      * @Serializer\Type("Billbee\CustomShopApi\Model\Address")
      */
-    public $deliveryAddress;
+    public ?Address $deliveryAddress = null;
 
     /**
-     * @var DateTime
      * @Serializer\SerializedName("order_date")
      * @Serializer\Type("DateTime")
      */
-    public $orderDate;
+    public ?DateTimeInterface $orderDate = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("email")
      * @Serializer\Type("string")
      */
-    public $email;
+    public ?string $email = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("phone1")
      * @Serializer\Type("string")
      */
-    public $phone1;
+    public ?string $phone1 = null;
 
     /**
-     * @var DateTime
      * @Serializer\SerializedName("pay_date")
      * @Serializer\Type("DateTime")
      */
-    public $payDate;
+    public ?DateTimeInterface $payDate = null;
 
     /**
-     * @var DateTime
      * @Serializer\SerializedName("ship_date")
      * @Serializer\Type("DateTime")
      */
-    public $shipDate;
+    public ?DateTimeInterface $shipDate = null;
 
     /**
-     * @var int
      * @Serializer\SerializedName("payment_method")
      * @Serializer\Type("int")
      */
-    public $paymentMethod;
+    public ?int $paymentMethod = null;
 
     /**
-     * @var int
      * @Serializer\SerializedName("order_status_id")
      * @Serializer\Type("int")
      */
-    public $statusId;
+    public ?int $statusId = null;
 
     /**
-     * @var OrderProduct[]
+     * @var ?OrderProduct[]
      * @Serializer\SerializedName("order_products")
      * @Serializer\Type("array<Billbee\CustomShopApi\Model\OrderProduct>")
      */
-    public $items;
+    public ?array $items = null;
 
     /**
-     * @var OrderComment[]
+     * @var ?OrderComment[]
      * @Serializer\SerializedName("order_history")
      * @Serializer\Type("array<Billbee\CustomShopApi\Model\OrderComment>")
      */
-    public $comments;
+    public ?array $comments = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("seller_comment")
      * @Serializer\Type("string")
      */
-    public $sellerComment;
+    public ?string $sellerComment = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("shippingprofile_id")
      * @Serializer\Type("string")
      */
-    public $shippingProfileId;
+    public ?string $shippingProfileId = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("vat_id")
      * @Serializer\Type("string")
      */
-    public $vatId;
+    public ?string $vatId = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("payment_transaction_id")
      * @Serializer\Type("string")
      */
-    public $paymentTransactionId;
+    public ?string $paymentTransactionId = null;
 
-    /**
-     * @return mixed
-     */
-    public function getOrderId()
+    public function getOrderId(): ?string
     {
         return $this->orderId;
     }
 
-    /**
-     * @param mixed $orderId
-     * @return Order
-     */
-    public function setOrderId($orderId)
+    public function setOrderId(?string $orderId): Order
     {
         $this->orderId = $orderId;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getOrderNumber()
+    public function getOrderNumber(): ?string
     {
         return $this->orderNumber;
     }
 
-    /**
-     * @param mixed $orderNumber
-     * @return Order
-     */
-    public function setOrderNumber($orderNumber)
+    public function setOrderNumber(?string $orderNumber): Order
     {
         $this->orderNumber = $orderNumber;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getCurrencyCode()
+    public function getCurrencyCode(): ?string
     {
         return $this->currencyCode;
     }
 
-    /**
-     * @param mixed $currencyCode
-     * @return Order
-     */
-    public function setCurrencyCode($currencyCode)
+    public function setCurrencyCode(?string $currencyCode): Order
     {
         $this->currencyCode = $currencyCode;
         return $this;
     }
 
-    /**
-     * @return string
-     */
-    public function getDeliverySourceCountryCode()
+    public function getDeliverySourceCountryCode(): ?string
     {
         return $this->deliverySourceCountryCode;
     }
 
-    /**
-     * @param string $deliverySourceCountryCode
-     * @return Order
-     */
-    public function setDeliverySourceCountryCode($deliverySourceCountryCode)
+    public function setDeliverySourceCountryCode(?string $deliverySourceCountryCode): Order
     {
         $this->deliverySourceCountryCode = $deliverySourceCountryCode;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getNickName()
+    public function getNickName(): ?string
     {
         return $this->nickName;
     }
 
-    /**
-     * @param mixed $nickName
-     * @return Order
-     */
-    public function setNickName($nickName)
+    public function setNickName(?string $nickName): Order
     {
         $this->nickName = $nickName;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getShipCost()
+    public function getShipCost(): ?float
     {
         return $this->shipCost;
     }
 
-    /**
-     * @param mixed $shipCost
-     * @return Order
-     */
-    public function setShipCost($shipCost)
+    public function setShipCost(?float $shipCost): Order
     {
         $this->shipCost = $shipCost;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getInvoiceAddress()
+    public function getInvoiceAddress(): ?Address
     {
         return $this->invoiceAddress;
     }
 
-    /**
-     * @param mixed $invoiceAddress
-     * @return Order
-     */
-    public function setInvoiceAddress($invoiceAddress)
+    public function setInvoiceAddress(?Address $invoiceAddress): Order
     {
         $this->invoiceAddress = $invoiceAddress;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getDeliveryAddress()
+    public function getDeliveryAddress(): ?Address
     {
         return $this->deliveryAddress;
     }
 
-    /**
-     * @param mixed $deliveryAddress
-     * @return Order
-     */
-    public function setDeliveryAddress($deliveryAddress)
+    public function setDeliveryAddress(?Address $deliveryAddress): Order
     {
         $this->deliveryAddress = $deliveryAddress;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getOrderDate()
+    public function getOrderDate(): ?DateTimeInterface
     {
         return $this->orderDate;
     }
 
-    /**
-     * @param mixed $orderDate
-     * @return Order
-     */
-    public function setOrderDate($orderDate)
+    public function setOrderDate(?DateTimeInterface $orderDate): Order
     {
         $this->orderDate = $orderDate;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getEmail()
+    public function getEmail(): ?string
     {
         return $this->email;
     }
 
-    /**
-     * @param mixed $email
-     * @return Order
-     */
-    public function setEmail($email)
+    public function setEmail(?string $email): Order
     {
         $this->email = $email;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getPhone1()
+    public function getPhone1(): ?string
     {
         return $this->phone1;
     }
 
-    /**
-     * @param mixed $phone1
-     * @return Order
-     */
-    public function setPhone1($phone1)
+    public function setPhone1(?string $phone1): Order
     {
         $this->phone1 = $phone1;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getPayDate()
+    public function getPayDate(): ?DateTimeInterface
     {
         return $this->payDate;
     }
 
-    /**
-     * @param mixed $payDate
-     * @return Order
-     */
-    public function setPayDate($payDate)
+    public function setPayDate(?DateTimeInterface $payDate): Order
     {
         $this->payDate = $payDate;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getShipDate()
+    public function getShipDate(): ?DateTimeInterface
     {
         return $this->shipDate;
     }
 
-    /**
-     * @param mixed $shipDate
-     * @return Order
-     */
-    public function setShipDate($shipDate)
+    public function setShipDate(?DateTimeInterface $shipDate): Order
     {
         $this->shipDate = $shipDate;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getPaymentMethod()
+    public function getPaymentMethod(): ?int
     {
         return $this->paymentMethod;
     }
 
-    /**
-     * @param mixed $paymentMethod
-     * @return Order
-     */
-    public function setPaymentMethod($paymentMethod)
+    public function setPaymentMethod(?int $paymentMethod): Order
     {
         $this->paymentMethod = $paymentMethod;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getStatusId()
+    public function getStatusId(): ?int
     {
         return $this->statusId;
     }
 
-    /**
-     * @param mixed $statusId
-     * @return Order
-     */
-    public function setStatusId($statusId)
+    public function setStatusId(?int $statusId): Order
     {
         $this->statusId = $statusId;
         return $this;
     }
 
     /**
-     * @return mixed
+     * @return ?OrderProduct[]
      */
-    public function getItems()
+    public function getItems(): ?array
     {
         return $this->items;
     }
 
     /**
-     * @param mixed $items
+     * @param ?OrderProduct[] $items
      * @return Order
      */
-    public function setItems($items)
+    public function setItems(?array $items): Order
     {
         $this->items = $items;
         return $this;
     }
 
     /**
-     * @return mixed
+     * @return ?OrderComment[]
      */
-    public function getComments()
+    public function getComments(): ?array
     {
         return $this->comments;
     }
 
     /**
-     * @param mixed $comments
+     * @param ?OrderComment[] $comments
      * @return Order
      */
-    public function setComments($comments)
+    public function setComments(?array $comments): Order
     {
         $this->comments = $comments;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getSellerComment()
+    public function getSellerComment(): ?string
     {
         return $this->sellerComment;
     }
 
-    /**
-     * @param mixed $sellerComment
-     * @return Order
-     */
-    public function setSellerComment($sellerComment)
+    public function setSellerComment(?string $sellerComment): Order
     {
         $this->sellerComment = $sellerComment;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getShippingProfileId()
+    public function getShippingProfileId(): ?string
     {
         return $this->shippingProfileId;
     }
 
-    /**
-     * @param mixed $shippingProfileId
-     * @return Order
-     */
-    public function setShippingProfileId($shippingProfileId)
+    public function setShippingProfileId(?string $shippingProfileId): Order
     {
         $this->shippingProfileId = $shippingProfileId;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getVatId()
+    public function getVatId(): ?string
     {
         return $this->vatId;
     }
 
-    /**
-     * @param mixed $vatId
-     * @return Order
-     */
-    public function setVatId($vatId)
+    public function setVatId(?string $vatId): Order
     {
         $this->vatId = $vatId;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getPaymentTransactionId()
+    public function getPaymentTransactionId(): ?string
     {
         return $this->paymentTransactionId;
     }
 
-    /**
-     * @param mixed $paymentTransactionId
-     * @return Order
-     */
-    public function setPaymentTransactionId($paymentTransactionId)
+    public function setPaymentTransactionId(?string $paymentTransactionId): Order
     {
         $this->paymentTransactionId = $paymentTransactionId;
         return $this;
diff --git a/src/Model/OrderComment.php b/src/Model/OrderComment.php
index e32f8f5..85d4a48 100644
--- a/src/Model/OrderComment.php
+++ b/src/Model/OrderComment.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -12,6 +12,7 @@
 
 namespace Billbee\CustomShopApi\Model;
 
+use DateTimeInterface;
 use JMS\Serializer\Annotation as Serializer;
 
 class OrderComment
@@ -20,93 +21,65 @@ class OrderComment
      * @Serializer\SerializedName("date_added")
      * @Serializer\Type("DateTime")
      */
-    public $dateAdded;
+    public ?DateTimeInterface $dateAdded = null;
 
     /**
      * @Serializer\SerializedName("name")
      * @Serializer\Type("string")
      */
-    public $name;
+    public ?string $name = null;
 
     /**
      * @Serializer\SerializedName("comment")
      * @Serializer\Type("string")
      */
-    public $comment;
+    public ?string $comment = null;
 
     /**
      * @Serializer\SerializedName("from_customer")
      * @Serializer\Type("bool")
      */
-    public $fromCustomer = false;
+    public bool $fromCustomer = false;
 
-    /**
-     * @return mixed
-     */
-    public function getDateAdded()
+    public function getDateAdded(): ?DateTimeInterface
     {
         return $this->dateAdded;
     }
 
-    /**
-     * @param mixed $dateAdded
-     * @return OrderComment
-     */
-    public function setDateAdded($dateAdded)
+    public function setDateAdded(?DateTimeInterface $dateAdded): OrderComment
     {
         $this->dateAdded = $dateAdded;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getName()
+    public function getName(): ?string
     {
         return $this->name;
     }
 
-    /**
-     * @param mixed $name
-     * @return OrderComment
-     */
-    public function setName($name)
+    public function setName(?string $name): OrderComment
     {
         $this->name = $name;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getComment()
+    public function getComment(): ?string
     {
         return $this->comment;
     }
 
-    /**
-     * @param mixed $comment
-     * @return OrderComment
-     */
-    public function setComment($comment)
+    public function setComment(?string $comment): OrderComment
     {
         $this->comment = $comment;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getFromCustomer()
+    public function getFromCustomer(): bool
     {
         return $this->fromCustomer;
     }
 
-    /**
-     * @param mixed $fromCustomer
-     * @return OrderComment
-     */
-    public function setFromCustomer($fromCustomer)
+    public function setFromCustomer(bool $fromCustomer): OrderComment
     {
         $this->fromCustomer = $fromCustomer;
         return $this;
diff --git a/src/Model/OrderProduct.php b/src/Model/OrderProduct.php
index e006980..26fb07c 100644
--- a/src/Model/OrderProduct.php
+++ b/src/Model/OrderProduct.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -20,189 +20,142 @@ class OrderProduct
      * @Serializer\SerializedName("discount_percent")
      * @Serializer\Type("float")
      */
-    public $discountPercent;
+    public ?float $discountPercent = null;
 
     /**
      * @Serializer\SerializedName("quantity")
      * @Serializer\Type("float")
      */
-    public $quantity;
+    public ?float $quantity = null;
 
     /**
      * @Serializer\SerializedName("unit_price")
      * @Serializer\Type("float")
      */
-    public $unitPrice;
+    public ?float $unitPrice = null;
 
     /**
      * @Serializer\SerializedName("product_id")
      * @Serializer\Type("string")
      */
-    public $productId;
+    public ?string $productId = null;
 
     /**
      * @Serializer\SerializedName("name")
      * @Serializer\Type("string")
      */
-    public $name;
+    public ?string $name = null;
 
     /**
      * @Serializer\SerializedName("sku")
      * @Serializer\Type("string")
      */
-    public $sku;
+    public ?string $sku = null;
 
     /**
      * @Serializer\SerializedName("tax_rate")
      * @Serializer\Type("float")
      */
-    public $taxRate;
+    public ?float $taxRate = null;
 
     /**
+     * @var OrderProductOption[]
      * @Serializer\SerializedName("options")
      * @Serializer\Type("array<Billbee\CustomShopApi\Model\OrderProductOption>")
      */
-    public $options;
+    public ?array $options = null;
 
-    /**
-     * @return mixed
-     */
-    public function getDiscountPercent()
+    public function getDiscountPercent(): ?float
     {
         return $this->discountPercent;
     }
 
-    /**
-     * @param mixed $discountPercent
-     * @return OrderProduct
-     */
-    public function setDiscountPercent($discountPercent)
+    public function setDiscountPercent(?float $discountPercent): OrderProduct
     {
         $this->discountPercent = $discountPercent;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getQuantity()
+    public function getQuantity(): ?float
     {
         return $this->quantity;
     }
 
-    /**
-     * @param mixed $quantity
-     * @return OrderProduct
-     */
-    public function setQuantity($quantity)
+    public function setQuantity(?float $quantity): OrderProduct
     {
         $this->quantity = $quantity;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getUnitPrice()
+
+    public function getUnitPrice(): ?float
     {
         return $this->unitPrice;
     }
 
-    /**
-     * @param mixed $unitPrice
-     * @return OrderProduct
-     */
-    public function setUnitPrice($unitPrice)
+    public function setUnitPrice(?float $unitPrice): OrderProduct
     {
         $this->unitPrice = $unitPrice;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getProductId()
+    public function getProductId(): ?string
     {
         return $this->productId;
     }
 
-    /**
-     * @param mixed $productId
-     * @return OrderProduct
-     */
-    public function setProductId($productId)
+    public function setProductId(?string $productId): OrderProduct
     {
         $this->productId = $productId;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getName()
+    public function getName(): ?string
     {
         return $this->name;
     }
 
-    /**
-     * @param mixed $name
-     * @return OrderProduct
-     */
-    public function setName($name)
+    public function setName(?string $name): OrderProduct
     {
         $this->name = $name;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getSku()
+    public function getSku(): ?string
     {
         return $this->sku;
     }
 
-    /**
-     * @param mixed $sku
-     * @return OrderProduct
-     */
-    public function setSku($sku)
+    public function setSku(?string $sku): OrderProduct
     {
         $this->sku = $sku;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getTaxRate()
+
+    public function getTaxRate(): ?float
     {
         return $this->taxRate;
     }
 
-    /**
-     * @param mixed $taxRate
-     * @return OrderProduct
-     */
-    public function setTaxRate($taxRate)
+    public function setTaxRate(?float $taxRate): OrderProduct
     {
         $this->taxRate = $taxRate;
         return $this;
     }
 
     /**
-     * @return mixed
+     * @return OrderProductOption[]|null
      */
-    public function getOptions()
+    public function getOptions(): ?array
     {
         return $this->options;
     }
 
     /**
-     * @param mixed $options
-     * @return OrderProduct
+     * @param OrderProductOption[]|null $options
      */
-    public function setOptions($options)
+    public function setOptions(?array $options): OrderProduct
     {
         $this->options = $options;
         return $this;
diff --git a/src/Model/OrderProductOption.php b/src/Model/OrderProductOption.php
index 882afb0..b482a13 100644
--- a/src/Model/OrderProductOption.php
+++ b/src/Model/OrderProductOption.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -20,51 +20,37 @@ class OrderProductOption
      * @Serializer\SerializedName("name")
      * @Serializer\Type("string")
      */
-    public $name;
+    public ?string $name;
 
     /**
      * @Serializer\SerializedName("value")
      * @Serializer\Type("string")
      */
-    public $value;
+    public ?string $value;
 
-    public function __construct($name = null, $value = null)
+    public function __construct(?string $name = null, ?string $value = null)
     {
         $this->name = $name;
         $this->value = $value;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getName()
+    public function getName(): ?string
     {
         return $this->name;
     }
 
-    /**
-     * @param mixed $name
-     * @return OrderProductOption
-     */
-    public function setName($name)
+    public function setName(?string $name): OrderProductOption
     {
         $this->name = $name;
         return $this;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getValue()
+    public function getValue(): ?string
     {
         return $this->value;
     }
 
-    /**
-     * @param mixed $value
-     * @return OrderProductOption
-     */
-    public function setValue($value)
+    public function setValue(?string $value): OrderProductOption
     {
         $this->value = $value;
         return $this;
diff --git a/src/Model/PagedData.php b/src/Model/PagedData.php
index 9cdfe2d..8c857fa 100644
--- a/src/Model/PagedData.php
+++ b/src/Model/PagedData.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -14,20 +14,22 @@
 
 use RuntimeException;
 
+/**
+ * @phpstan-template T
+ */
 class PagedData
 {
-    /** @var array */
-    protected $data;
+    /** @var T[]  */
+    protected array $data;
 
-    /** @var int */
-    protected $totalCount;
+    protected int $totalCount;
 
     /**
      * PagedData constructor.
-     * @param array $data
+     * @param T[] $data
      * @param int $totalCount
      */
-    public function __construct(array $data = [], $totalCount = 0)
+    public function __construct(array $data = [], int $totalCount = 0)
     {
         $this->data = $data;
         $this->totalCount = $totalCount;
@@ -38,17 +40,14 @@ public function __construct(array $data = [], $totalCount = 0)
     }
 
     /**
-     * @return array
+     * @return T[]
      */
-    public function getData()
+    public function getData(): array
     {
         return $this->data;
     }
 
-    /**
-     * @return int
-     */
-    public function getTotalCount()
+    public function getTotalCount(): int
     {
         return $this->totalCount;
     }
diff --git a/src/Model/Pagination.php b/src/Model/Pagination.php
index 84c6dbb..7d801db 100644
--- a/src/Model/Pagination.php
+++ b/src/Model/Pagination.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -20,48 +20,57 @@ class Pagination
      * @Serializer\SerializedName("page")
      * @Serializer\Type("int")
      */
-    public $page;
+    public int $page = 1;
 
     /**
      * @Serializer\SerializedName("totalCount")
      * @Serializer\Type("int")
      */
-    public $totalCount;
+    public int $totalCount = 0;
 
     /**
      * @Serializer\SerializedName("totalPages")
      * @Serializer\Type("int")
      */
-    public $totalPages;
+    public int $totalPages = 0;
 
-    public function __construct($page = 1, $pageSize = 100, $totalCount = 0)
+    public function __construct(int $page = 1, int $pageSize = 100, int $totalCount = 0)
     {
         $this->page = $page;
-        $this->totalPages = ceil($totalCount / $pageSize);
+        $this->totalPages = (int)ceil($totalCount / $pageSize);
         $this->totalCount = $totalCount;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getPage()
+    public function getPage(): int
     {
         return $this->page;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getTotalCount()
+    public function setPage(int $page): Pagination
+    {
+        $this->page = $page;
+        return $this;
+    }
+
+    public function getTotalCount(): int
     {
         return $this->totalCount;
     }
 
-    /**
-     * @return mixed
-     */
-    public function getTotalPages()
+    public function setTotalCount(int $totalCount): Pagination
+    {
+        $this->totalCount = $totalCount;
+        return $this;
+    }
+
+    public function getTotalPages(): int
     {
         return $this->totalPages;
     }
+
+    public function setTotalPages(int $totalPages): Pagination
+    {
+        $this->totalPages = $totalPages;
+        return $this;
+    }
 }
diff --git a/src/Model/Product.php b/src/Model/Product.php
index cf91a62..057b212 100644
--- a/src/Model/Product.php
+++ b/src/Model/Product.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -17,475 +17,338 @@
 class Product
 {
     /**
-     * @var string
      * @Serializer\SerializedName("material")
      * @Serializer\Type("string")
      */
-    public $material;
+    public ?string $material = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("shortdescription")
      * @Serializer\Type("string")
      */
-    public $shortDescription;
+    public ?string $shortDescription = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("basic_attributes")
      * @Serializer\Type("string")
      */
-    public $basicAttributes;
+    public ?string $basicAttributes = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("description")
      * @Serializer\Type("string")
      */
-    public $description;
+    public ?string $description = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("id")
      * @Serializer\Type("string")
      */
-    public $id;
+    public ?string $id = null;
 
     /**
-     * @var ProductImage[]
+     * @var ?ProductImage[]
      * @Serializer\SerializedName("images")
      * @Serializer\Type("array<Billbee\CustomShopApi\Model\ProductImage>")
      */
-    public $images;
+    public ?array $images = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("title")
      * @Serializer\Type("string")
      */
-    public $title;
+    public ?string $title = null;
 
     /**
-     * @var float
      * @Serializer\SerializedName("price")
      * @Serializer\Type("float")
      */
-    public $price;
+    public ?float $price = null;
 
     /**
-     * @var float
      * @Serializer\SerializedName("quantity")
      * @Serializer\Type("float")
      */
-    public $quantity;
+    public ?float $quantity = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("sku")
      * @Serializer\Type("string")
      */
-    public $sku;
+    public ?string $sku = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("ean")
      * @Serializer\Type("string")
      */
-    public $ean;
+    public ?string $ean = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("manufacturer")
      * @Serializer\Type("string")
      */
-    public $manufacturer;
+    public ?string $manufacturer = null;
 
     /**
      * @var bool
      * @Serializer\SerializedName("isdigital")
      * @Serializer\Type("bool")
      */
-    public $isDigital = false;
+    public bool $isDigital = false;
 
     /**
-     * @var float
      * @Serializer\SerializedName("weight")
      * @Serializer\Type("float")
      */
-    public $weightInKg;
+    public ?float $weightInKg = null;
 
     /**
-     * @var float
      * @Serializer\SerializedName("vat_rate")
      * @Serializer\Type("float")
      */
-    public $vatRate;
+    public ?float $vatRate = null;
 
     /**
-     * @var float
      * @Serializer\SerializedName("lengthcm")
      * @Serializer\Type("float")
      */
-    public $lengthInCm;
+    public ?float $lengthInCm = null;
 
     /**
-     * @var float
      * @Serializer\SerializedName("widthcm")
      * @Serializer\Type("float")
      */
-    public $widthInCm;
+    public ?float $widthInCm = null;
 
     /**
-     * @var float
      * @Serializer\SerializedName("heightcm")
      * @Serializer\Type("float")
      */
-    public $heightInCm;
+    public ?float $heightInCm = null;
 
     /**
-     * @var array
+     * @var array<string, string>
      * @Serializer\SerializedName("customfields")
      * @Serializer\Type("array<string, string>")
      */
-    public $customFields;
+    public ?array $customFields = null;
 
-    /**
-     * @return string
-     */
-    public function getMaterial()
+    public function getMaterial(): ?string
     {
         return $this->material;
     }
 
-    /**
-     * @param string $material
-     * @return Product
-     */
-    public function setMaterial($material)
+    public function setMaterial(?string $material): Product
     {
         $this->material = $material;
         return $this;
     }
 
-    /**
-     * @return string
-     */
-    public function getShortDescription()
+    public function getShortDescription(): ?string
     {
         return $this->shortDescription;
     }
 
-    /**
-     * @param string $shortDescription
-     * @return Product
-     */
-    public function setShortDescription($shortDescription)
+    public function setShortDescription(?string $shortDescription): Product
     {
         $this->shortDescription = $shortDescription;
         return $this;
     }
 
-    /**
-     * @return string
-     */
-    public function getBasicAttributes()
+    public function getBasicAttributes(): ?string
     {
         return $this->basicAttributes;
     }
 
-    /**
-     * @param string $basicAttributes
-     * @return Product
-     */
-    public function setBasicAttributes($basicAttributes)
+    public function setBasicAttributes(?string $basicAttributes): Product
     {
         $this->basicAttributes = $basicAttributes;
         return $this;
     }
 
-    /**
-     * @return string
-     */
-    public function getDescription()
+    public function getDescription(): ?string
     {
         return $this->description;
     }
 
-    /**
-     * @param string $description
-     * @return Product
-     */
-    public function setDescription($description)
+    public function setDescription(?string $description): Product
     {
         $this->description = $description;
         return $this;
     }
 
-    /**
-     * @return string
-     */
-    public function getId()
+    public function getId(): ?string
     {
         return $this->id;
     }
 
-    /**
-     * @param string $id
-     * @return Product
-     */
-    public function setId($id)
+    public function setId(?string $id): Product
     {
         $this->id = $id;
         return $this;
     }
 
     /**
-     * @return ProductImage[]
+     * @return ?ProductImage[]
      */
-    public function getImages()
+    public function getImages(): ?array
     {
         return $this->images;
     }
 
     /**
-     * @param ProductImage[] $images
-     * @return Product
+     * @param ?ProductImage[] $images
      */
-    public function setImages($images)
+    public function setImages(?array $images): self
     {
         $this->images = $images;
         return $this;
     }
 
-    /**
-     * @return string
-     */
-    public function getTitle()
+    public function getTitle(): ?string
     {
         return $this->title;
     }
 
-    /**
-     * @param string $title
-     * @return Product
-     */
-    public function setTitle($title)
+    public function setTitle(?string $title): Product
     {
         $this->title = $title;
         return $this;
     }
 
-    /**
-     * @return float
-     */
-    public function getPrice()
+    public function getPrice(): ?float
     {
         return $this->price;
     }
 
-    /**
-     * @param float $price
-     * @return Product
-     */
-    public function setPrice($price)
+    public function setPrice(?float $price): Product
     {
-        $this->price = (float)$price;
+        $this->price = $price;
         return $this;
     }
 
-    /**
-     * @return float
-     */
-    public function getQuantity()
+    public function getQuantity(): ?float
     {
         return $this->quantity;
     }
 
-    /**
-     * @param float $quantity
-     * @return Product
-     */
-    public function setQuantity($quantity)
+    public function setQuantity(?float $quantity): Product
     {
-        $this->quantity = (float)$quantity;
+        $this->quantity = $quantity;
         return $this;
     }
 
-    /**
-     * @return string
-     */
-    public function getSku()
+    public function getSku(): ?string
     {
         return $this->sku;
     }
 
-    /**
-     * @param string $sku
-     * @return Product
-     */
-    public function setSku($sku)
+    public function setSku(?string $sku): Product
     {
         $this->sku = $sku;
         return $this;
     }
 
-    /**
-     * @return string
-     */
-    public function getEan()
+    public function getEan(): ?string
     {
         return $this->ean;
     }
 
-    /**
-     * @param string $ean
-     * @return Product
-     */
-    public function setEan($ean)
+    public function setEan(?string $ean): Product
     {
         $this->ean = $ean;
         return $this;
     }
 
-    /**
-     * @return string
-     */
-    public function getManufacturer()
+    public function getManufacturer(): ?string
     {
         return $this->manufacturer;
     }
 
-    /**
-     * @param string $manufacturer
-     * @return Product
-     */
-    public function setManufacturer($manufacturer)
+    public function setManufacturer(?string $manufacturer): Product
     {
         $this->manufacturer = $manufacturer;
         return $this;
     }
 
-    /**
-     * @return bool
-     */
-    public function isDigital()
+    public function isDigital(): bool
     {
         return $this->isDigital;
     }
 
-    /**
-     * @param bool $isDigital
-     * @return Product
-     */
-    public function setIsDigital($isDigital)
+    public function setIsDigital(bool $isDigital): Product
     {
         $this->isDigital = $isDigital;
         return $this;
     }
 
-    /**
-     * @return float
-     */
-    public function getWeightInKg()
+    public function getWeightInKg(): ?float
     {
         return $this->weightInKg;
     }
 
-    /**
-     * @param float $weightInKg
-     * @return Product
-     */
-    public function setWeightInKg($weightInKg)
+    public function setWeightInKg(?float $weightInKg): Product
     {
-        $this->weightInKg = (float)$weightInKg;
+        $this->weightInKg = $weightInKg;
         return $this;
     }
 
-    /**
-     * @return float
-     */
-    public function getVatRate()
+    public function getVatRate(): ?float
     {
         return $this->vatRate;
     }
 
-    /**
-     * @param float $vatRate
-     * @return Product
-     */
-    public function setVatRate($vatRate)
+    public function setVatRate(?float $vatRate): Product
     {
-        $this->vatRate = (float)$vatRate;
+        $this->vatRate = $vatRate;
         return $this;
     }
 
-    /**
-     * @return float
-     */
-    public function getLengthInCm()
+    public function getLengthInCm(): ?float
     {
         return $this->lengthInCm;
     }
 
-    /**
-     * @param float $lengthInCm
-     * @return Product
-     */
-    public function setLengthInCm($lengthInCm)
+    public function setLengthInCm(?float $lengthInCm): Product
     {
-        $this->lengthInCm = (float)$lengthInCm;
+        $this->lengthInCm = $lengthInCm;
         return $this;
     }
 
-    /**
-     * @return float
-     */
-    public function getWidthInCm()
+    public function getWidthInCm(): ?float
     {
         return $this->widthInCm;
     }
 
-    /**
-     * @param float $widthInCm
-     * @return Product
-     */
-    public function setWidthInCm($widthInCm)
+    public function setWidthInCm(?float $widthInCm): Product
     {
-        $this->widthInCm = (float)$widthInCm;
+        $this->widthInCm = $widthInCm;
         return $this;
     }
 
-    /**
-     * @return float
-     */
-    public function getHeightInCm()
+    public function getHeightInCm(): ?float
     {
         return $this->heightInCm;
     }
 
-    /**
-     * @param float $heightInCm
-     * @return Product
-     */
-    public function setHeightInCm($heightInCm)
+    public function setHeightInCm(?float $heightInCm): Product
     {
-        $this->heightInCm = (float)$heightInCm;
+        $this->heightInCm = $heightInCm;
         return $this;
     }
 
     /**
-     * @return array
+     * @return array<string, string>
      */
-    public function getCustomFields()
+    public function getCustomFields(): ?array
     {
         return $this->customFields;
     }
 
     /**
-     * @param array $customFields
-     * @return Product
+     * @param ?array<string, string> $customFields
      */
-    public function setCustomFields($customFields)
+    public function setCustomFields(?array $customFields): Product
     {
         $this->customFields = $customFields;
         return $this;
diff --git a/src/Model/ProductImage.php b/src/Model/ProductImage.php
index 561697d..cbce9cc 100644
--- a/src/Model/ProductImage.php
+++ b/src/Model/ProductImage.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -17,75 +17,51 @@
 class ProductImage
 {
     /**
-     * @var string
      * @Serializer\SerializedName("url")
      * @Serializer\Type("string")
      */
-    public $url;
+    public ?string $url = null;
 
     /**
-     * @var bool
      * @Serializer\SerializedName("isDefault")
      * @Serializer\Type("bool")
      */
-    public $isDefault = false;
+    public bool $isDefault = false;
 
     /**
-     * @var int
      * @Serializer\SerializedName("Position")
      * @Serializer\Type("int")
      */
-    public $position;
+    public ?int $position = null;
 
-    /**
-     * @return string
-     */
-    public function getUrl()
+    public function getUrl(): ?string
     {
         return $this->url;
     }
 
-    /**
-     * @param string $url
-     * @return ProductImage
-     */
-    public function setUrl($url)
+    public function setUrl(?string $url): ProductImage
     {
         $this->url = $url;
         return $this;
     }
 
-    /**
-     * @return bool
-     */
-    public function isDefault()
+    public function isDefault(): bool
     {
         return $this->isDefault;
     }
 
-    /**
-     * @param bool $isDefault
-     * @return ProductImage
-     */
-    public function setIsDefault($isDefault)
+    public function setIsDefault(bool $isDefault): ProductImage
     {
         $this->isDefault = $isDefault;
         return $this;
     }
 
-    /**
-     * @return int
-     */
-    public function getPosition()
+    public function getPosition(): ?int
     {
         return $this->position;
     }
 
-    /**
-     * @param int $position
-     * @return ProductImage
-     */
-    public function setPosition($position)
+    public function setPosition(?int $position): ProductImage
     {
         $this->position = (int)$position;
         return $this;
diff --git a/src/Model/Response/GetOrdersResponse.php b/src/Model/Response/GetOrdersResponse.php
index b802ec4..b4e2efb 100644
--- a/src/Model/Response/GetOrdersResponse.php
+++ b/src/Model/Response/GetOrdersResponse.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -23,25 +23,26 @@ class GetOrdersResponse
      * @Serializer\SerializedName("paging")
      * @Serializer\Type("Billbee\CustomShopApi\Model\Pagination")
      */
-    protected $paging;
+    protected Pagination $paging;
 
     /**
      * @var Order[]
      * @Serializer\SerializedName("orders")
      * @Serializer\Type("array<Billbee\CustomShopApi\Model\Order>")
      */
-    protected $orders;
+    protected array $orders = [];
 
+    /**
+     * @param Pagination $paging
+     * @param Order[] $orders
+     */
     public function __construct(Pagination $paging, $orders = [])
     {
         $this->paging = $paging;
         $this->orders = $orders;
     }
 
-    /**
-     * @return Pagination
-     */
-    public function getPaging()
+    public function getPaging(): Pagination
     {
         return $this->paging;
     }
@@ -49,7 +50,7 @@ public function getPaging()
     /**
      * @return Order[]
      */
-    public function getOrders()
+    public function getOrders(): array
     {
         return $this->orders;
     }
diff --git a/src/Model/Response/GetProductsResponse.php b/src/Model/Response/GetProductsResponse.php
index 02c7aae..e7451ae 100644
--- a/src/Model/Response/GetProductsResponse.php
+++ b/src/Model/Response/GetProductsResponse.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -19,29 +19,29 @@
 class GetProductsResponse
 {
     /**
-     * @var Pagination
      * @Serializer\SerializedName("paging")
      * @Serializer\Type("Billbee\CustomShopApi\Model\Pagination")
      */
-    protected $paging;
+    protected Pagination $paging;
 
     /**
-     * @var Product[]
+     * @var array<Product>
      * @Serializer\SerializedName("products")
      * @Serializer\Type("array<Billbee\CustomShopApi\Model\Product>")
      */
-    protected $products;
+    protected array $products = [];
 
-    public function __construct($paging, $products)
+    /**
+     * @param Pagination $paging
+     * @param Product[] $products
+     */
+    public function __construct(Pagination $paging, array $products)
     {
         $this->paging = $paging;
         $this->products = $products;
     }
 
-    /**
-     * @return Pagination
-     */
-    public function getPaging()
+    public function getPaging(): Pagination
     {
         return $this->paging;
     }
@@ -49,7 +49,7 @@ public function getPaging()
     /**
      * @return Product[]
      */
-    public function getProducts()
+    public function getProducts(): array
     {
         return $this->products;
     }
diff --git a/src/Model/ShippingProfile.php b/src/Model/ShippingProfile.php
index 48b22f4..49d65ed 100644
--- a/src/Model/ShippingProfile.php
+++ b/src/Model/ShippingProfile.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -17,56 +17,40 @@
 class ShippingProfile
 {
     /**
-     * @var string
      * @Serializer\SerializedName("Id")
      * @Serializer\Type("string")
      */
-    public $id;
+    public ?string $id = null;
 
     /**
-     * @var string
      * @Serializer\SerializedName("Name")
      * @Serializer\Type("string")
      */
-    public $name;
+    public ?string $name = null;
 
-    public function __construct($id = null, $name = null)
+    public function __construct(?string $id = null, ?string $name = null)
     {
         $this->id = $id;
         $this->name = $name;
     }
 
-    /**
-     * @return string
-     */
-    public function getId()
+    public function getId(): ?string
     {
         return $this->id;
     }
 
-    /**
-     * @param string $id
-     * @return ShippingProfile
-     */
-    public function setId($id)
+    public function setId(?string $id): ShippingProfile
     {
         $this->id = $id;
         return $this;
     }
 
-    /**
-     * @return string
-     */
-    public function getName()
+    public function getName(): ?string
     {
         return $this->name;
     }
 
-    /**
-     * @param string $name
-     * @return ShippingProfile
-     */
-    public function setName($name)
+    public function setName(?string $name): ShippingProfile
     {
         $this->name = $name;
         return $this;
diff --git a/src/Repository/OrdersRepositoryInterface.php b/src/Repository/OrdersRepositoryInterface.php
index 35975f2..d374c75 100644
--- a/src/Repository/OrdersRepositoryInterface.php
+++ b/src/Repository/OrdersRepositoryInterface.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -30,7 +30,7 @@ interface OrdersRepositoryInterface extends RepositoryInterface
      * @throws NotImplementedException If the method is not implemented
      * @throws OrderNotFoundException If the order wasn't found
      */
-    public function getOrder($orderId);
+    public function getOrder(string $orderId): Order;
 
     /**
      * Should return the orders which are created or modified since the $modifiedSince parameter.
@@ -38,9 +38,9 @@ public function getOrder($orderId);
      * @param int $page The page, 1 is the first page.
      * @param int $pageSize The number of orders per page
      * @param DateTime $modifiedSince The date from which the orders should be returned.
-     * @return PagedData A PagedData object which holds the found orders
+     * @return PagedData<Order> A PagedData object which holds the found orders
      */
-    public function getOrders($page, $pageSize, DateTime $modifiedSince);
+    public function getOrders(int $page, int $pageSize, DateTime $modifiedSince): PagedData;
 
     /**
      * Billbee calls this method to acknowledge that the order was received
@@ -52,19 +52,19 @@ public function getOrders($page, $pageSize, DateTime $modifiedSince);
      * @throws OrderNotFoundException If the order was not found
      * @throws Exception If something went wrong
      */
-    public function acknowledgeOrder($orderId);
+    public function acknowledgeOrder(string $orderId);
 
     /**
      * Sets the state of an order
      *
      * @param string $orderId The id of the order
      * @param int $newStateId The new state id of the order
-     * @param string $comment A comment
+     * @param ?string $comment A comment
      * @return void
      *
      * @throws NotImplementedException If the method is not implemented
      * @throws OrderNotFoundException If the order was not found
      * @throws Exception If something went wrong
      */
-    public function setOrderState($orderId, $newStateId, $comment);
+    public function setOrderState(string $orderId, int $newStateId, ?string $comment);
 }
diff --git a/src/Repository/ProductsRepositoryInterface.php b/src/Repository/ProductsRepositoryInterface.php
index ac41f55..df06184 100644
--- a/src/Repository/ProductsRepositoryInterface.php
+++ b/src/Repository/ProductsRepositoryInterface.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -24,11 +24,11 @@ interface ProductsRepositoryInterface extends RepositoryInterface
      *
      * @param int $page The page, 1 is the first page.
      * @param int $pageSize The number of products per page
-     * @return PagedData A PagedData object which holds the found products
+     * @return PagedData<Product> A PagedData object which holds the found products
      *
      * @throws NotImplementedException If the method is not implemented
      */
-    public function getProducts($page, $pageSize);
+    public function getProducts(int $page, int $pageSize): PagedData;
 
     /**
      * Returns a single product by the id
@@ -39,5 +39,5 @@ public function getProducts($page, $pageSize);
      * @throws NotImplementedException If the method is not implemented
      * @throws ProductNotFoundException If the product does not exist
      */
-    public function getProduct($productId);
+    public function getProduct(string $productId): Product;
 }
diff --git a/src/Repository/RepositoryInterface.php b/src/Repository/RepositoryInterface.php
index 75e9d8b..7bceca3 100644
--- a/src/Repository/RepositoryInterface.php
+++ b/src/Repository/RepositoryInterface.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
diff --git a/src/Repository/ShippingProfileRepositoryInterface.php b/src/Repository/ShippingProfileRepositoryInterface.php
index 56b4b71..b566024 100644
--- a/src/Repository/ShippingProfileRepositoryInterface.php
+++ b/src/Repository/ShippingProfileRepositoryInterface.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -21,8 +21,7 @@ interface ShippingProfileRepositoryInterface extends RepositoryInterface
      * Return all available shipping profiles
      *
      * @return ShippingProfile[] The shipping profiles
-     *
      * @throws NotImplementedException If the method is not implemented
      */
-    public function getShippingProfiles();
+    public function getShippingProfiles(): array;
 }
diff --git a/src/Repository/StockSyncRepositoryInterface.php b/src/Repository/StockSyncRepositoryInterface.php
index e8ffdd5..d29d783 100644
--- a/src/Repository/StockSyncRepositoryInterface.php
+++ b/src/Repository/StockSyncRepositoryInterface.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -29,5 +29,5 @@ interface StockSyncRepositoryInterface extends RepositoryInterface
      * @throws ProductNotFoundException If the product does not exist
      * @throws Exception If something went wrong
      */
-    public function setStock($productId, $quantity);
+    public function setStock(string $productId, float $quantity): void;
 }
diff --git a/src/RequestHandler/OrderRequestHandler.php b/src/RequestHandler/OrderRequestHandler.php
index d0a2b57..ce13c4c 100644
--- a/src/RequestHandler/OrderRequestHandler.php
+++ b/src/RequestHandler/OrderRequestHandler.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -24,8 +24,7 @@
 
 class OrderRequestHandler extends RequestHandlerBase
 {
-    /** @var OrdersRepositoryInterface */
-    private $ordersRepository;
+    private OrdersRepositoryInterface $ordersRepository;
 
     public function __construct(OrdersRepositoryInterface $ordersRepository)
     {
@@ -33,7 +32,12 @@ public function __construct(OrdersRepositoryInterface $ordersRepository)
         $this->supportedActions = ['GetOrders', 'AckOrder', 'GetOrder', 'SetOrderState'];
     }
 
-    public function handle(RequestInterface $request, $queryArgs = [])
+    /**
+     * @param RequestInterface $request
+     * @param array<string, string> $queryArgs
+     * @return Response
+     */
+    public function handle(RequestInterface $request, array $queryArgs = []): Response
     {
         if (isset($queryArgs['Action'])) {
             if ($queryArgs['Action'] == 'GetOrders') {
@@ -53,15 +57,20 @@ public function handle(RequestInterface $request, $queryArgs = [])
             }
         }
 
-        return null;
+        return Response::notImplemented();
     }
 
-    private function getOrders($arguments)
+    /**
+     * @param array<string, string> $arguments
+     * @return Response
+     */
+    private function getOrders(array $arguments): Response
     {
+        /*** @var array{"Page": ?string, "PageSize": ?string, "StartDate": ?string} $arguments */
         $page = isset($arguments['Page']) ? (int)$arguments['Page'] : 1;
         $pageSize = isset($arguments['PageSize']) ? (int)$arguments['PageSize'] : 1;
         try {
-            $startDate = new DateTime(isset($arguments['StartDate']) ? $arguments['StartDate'] : '-30 days');
+            $startDate = new DateTime($arguments['StartDate'] ?? '-30 days');
         } catch (Exception $e) {
             return Response::internalServerError("Der Wert {$arguments['StartDate']} konnte nicht in eine gültiges Datum umgewandelt werden.");
         }
@@ -73,8 +82,9 @@ private function getOrders($arguments)
         return Response::json($response);
     }
 
-    private function ackOrder($request)
+    private function ackOrder(RequestInterface $request): Response
     {
+        /** @var array{"OrderId": ?string} $data */
         $data = $this->deserializeBody($request);
 
         if (!isset($data['OrderId']) || empty($orderId = trim($data['OrderId']))) {
@@ -91,8 +101,13 @@ private function ackOrder($request)
         }
     }
 
-    private function getOrder($arguments)
+    /**
+     * @param array<string, string> $arguments
+     * @return Response
+     */
+    private function getOrder(array $arguments): Response
     {
+        /** @var array{"OrderId": ?string} $arguments */
         if (!isset($arguments['OrderId']) || empty($orderId = trim($arguments['OrderId']))) {
             return Response::badRequest('Es wurde keine OrderId übergeben');
         }
@@ -106,8 +121,9 @@ private function getOrder($arguments)
         }
     }
 
-    private function setOrderState(RequestInterface $request)
+    private function setOrderState(RequestInterface $request): Response
     {
+        /** @var array{"OrderId": ?string, "NewStateTypeId": ?string, "Comment": ?string} $data */
         $data = $this->deserializeBody($request);
 
         if (!isset($data['OrderId']) || empty($orderId = trim($data['OrderId']))) {
@@ -119,7 +135,7 @@ private function setOrderState(RequestInterface $request)
         };
 
 
-        $comment = isset($data['Comment']) ? $data['Comment'] : "";
+        $comment = $data['Comment'] ?? "";
 
         try {
             $this->ordersRepository->setOrderState($orderId, $newStateId, $comment);
@@ -131,10 +147,7 @@ private function setOrderState(RequestInterface $request)
         }
     }
 
-    /**
-     * @return Response
-     */
-    private function createOrderNotFoundResponse()
+    private function createOrderNotFoundResponse(): Response
     {
         return Response::notFound('Die Bestellung wurde nicht gefunden');
     }
diff --git a/src/RequestHandler/ProductRequestHandler.php b/src/RequestHandler/ProductRequestHandler.php
index e4fc54b..f49d1ab 100644
--- a/src/RequestHandler/ProductRequestHandler.php
+++ b/src/RequestHandler/ProductRequestHandler.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -22,8 +22,7 @@
 
 class ProductRequestHandler extends RequestHandlerBase
 {
-    /** @var ProductsRepositoryInterface */
-    private $productsRepository;
+    private ProductsRepositoryInterface $productsRepository;
 
     public function __construct(ProductsRepositoryInterface $productsRepository)
     {
@@ -31,21 +30,32 @@ public function __construct(ProductsRepositoryInterface $productsRepository)
         $this->supportedActions = ['GetProduct', 'GetProducts'];
     }
 
-    public function handle(RequestInterface $request, $queryArgs = [])
+    /**
+     * @param RequestInterface $request
+     * @param array<string, string> $queryArgs
+     * @return Response
+     */
+    public function handle(RequestInterface $request, array $queryArgs = []): Response
     {
-        if ($queryArgs['Action'] == 'GetProduct') {
-            return $this->getProduct($queryArgs);
-        }
+        if (isset($queryArgs['Action'])) {
+            if ($queryArgs['Action'] == 'GetProduct') {
+                return $this->getProduct($queryArgs);
+            }
 
-        if ($queryArgs['Action'] == 'GetProducts') {
-            return $this->getProducts($queryArgs);
+            if ($queryArgs['Action'] == 'GetProducts') {
+                return $this->getProducts($queryArgs);
+            }
         }
-
-        return null;
+        return Response::notImplemented();
     }
 
-    private function getProduct($queryArgs)
+    /**
+     * @param array<string, string> $queryArgs
+     * @return Response
+     */
+    private function getProduct(array $queryArgs): Response
     {
+        /** @var array{"ProductId": ?string} $queryArgs */
         if (!isset($queryArgs['ProductId']) || empty($productId = trim($queryArgs['ProductId']))) {
             return Response::badRequest('Es wurde keine ProductId übergeben');
         }
@@ -60,8 +70,13 @@ private function getProduct($queryArgs)
         }
     }
 
-    private function getProducts($queryArgs)
+    /**
+     * @param array<string, string> $queryArgs
+     * @return Response
+     */
+    private function getProducts(array $queryArgs): Response
     {
+        /** @var array{"Page": ?string, "PageSize": ?string} $queryArgs */
         $page = isset($queryArgs['Page']) ? (int)$queryArgs['Page'] : 1;
         $pageSize = isset($queryArgs['PageSize']) ? (int)$queryArgs['PageSize'] : 100;
 
diff --git a/src/RequestHandler/RequestHandlerBase.php b/src/RequestHandler/RequestHandlerBase.php
index 7f5f9ba..2b9ea7d 100644
--- a/src/RequestHandler/RequestHandlerBase.php
+++ b/src/RequestHandler/RequestHandlerBase.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -17,16 +17,18 @@
 
 abstract class RequestHandlerBase implements RequestHandlerInterface
 {
-    protected $supportedActions = [];
+    /** @var string[] */
+    protected array $supportedActions = [];
 
-    protected function deserializeBody(RequestInterface $request)
+    /** @return array<string, mixed> */
+    protected function deserializeBody(RequestInterface $request): array
     {
         $requestBody = (string)$request->getBody();
         parse_str($requestBody, $deserializedBody);
         return $deserializedBody;
     }
 
-    public function canHandle(RequestInterface $request, $queryArgs = [])
+    public function canHandle(RequestInterface $request, array $queryArgs = []): bool
     {
         return in_array($queryArgs['Action'], $this->supportedActions);
     }
diff --git a/src/RequestHandler/ShippingProfileRequestHandler.php b/src/RequestHandler/ShippingProfileRequestHandler.php
index 8032d11..30044f5 100644
--- a/src/RequestHandler/ShippingProfileRequestHandler.php
+++ b/src/RequestHandler/ShippingProfileRequestHandler.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -19,8 +19,7 @@
 
 class ShippingProfileRequestHandler extends RequestHandlerBase
 {
-    /** @var ShippingProfileRepositoryInterface */
-    private $shippingProfileRepository;
+    private ShippingProfileRepositoryInterface $shippingProfileRepository;
 
     public function __construct(ShippingProfileRepositoryInterface $shippingProfileRepository)
     {
@@ -28,16 +27,16 @@ public function __construct(ShippingProfileRepositoryInterface $shippingProfileR
         $this->shippingProfileRepository = $shippingProfileRepository;
     }
 
-    public function handle(RequestInterface $request, $queryArgs = [])
+    public function handle(RequestInterface $request, array $queryArgs = []): Response
     {
         if ($queryArgs['Action'] == 'GetShippingProfiles') {
             return $this->getShippingProfiles();
         }
 
-        return null;
+        return Response::notImplemented();
     }
 
-    private function getShippingProfiles()
+    private function getShippingProfiles(): Response
     {
         try {
             $profiles = $this->shippingProfileRepository->getShippingProfiles();
diff --git a/src/RequestHandler/StockRequestHandler.php b/src/RequestHandler/StockRequestHandler.php
index dea99e1..89c675c 100644
--- a/src/RequestHandler/StockRequestHandler.php
+++ b/src/RequestHandler/StockRequestHandler.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -21,8 +21,7 @@
 
 class StockRequestHandler extends RequestHandlerBase
 {
-    /** @var StockSyncRepositoryInterface */
-    private $stockSyncRepository;
+    private StockSyncRepositoryInterface $stockSyncRepository;
 
     public function __construct(StockSyncRepositoryInterface $stockSyncRepository)
     {
@@ -30,17 +29,18 @@ public function __construct(StockSyncRepositoryInterface $stockSyncRepository)
         $this->supportedActions = ['SetStock'];
     }
 
-    public function handle(RequestInterface $request, $queryArgs = [])
+    public function handle(RequestInterface $request, array $queryArgs = []): Response
     {
         if ($queryArgs['Action'] == 'SetStock') {
             return $this->setStock($request);
         }
 
-        return null;
+        return Response::notImplemented();
     }
 
-    private function setStock(RequestInterface $request)
+    private function setStock(RequestInterface $request): Response
     {
+        /** @var array{"ProductId": ?string, "AvailableStock": ?string} $data */
         $data = $this->deserializeBody($request);
         if (!isset($data['ProductId']) || empty($productId = trim($data['ProductId']))) {
             return Response::badRequest('Es wurde keine ProductId übergeben');
diff --git a/src/Security/AuthenticatorInterface.php b/src/Security/AuthenticatorInterface.php
index 536cfec..c29ef7b 100644
--- a/src/Security/AuthenticatorInterface.php
+++ b/src/Security/AuthenticatorInterface.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -16,5 +16,5 @@
 
 interface AuthenticatorInterface
 {
-    public function isAuthorized(RequestInterface $request);
+    public function isAuthorized(RequestInterface $request): bool;
 }
diff --git a/src/Security/KeyAuthenticator.php b/src/Security/KeyAuthenticator.php
index adf0d9a..6875e6c 100644
--- a/src/Security/KeyAuthenticator.php
+++ b/src/Security/KeyAuthenticator.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -16,22 +16,22 @@
 
 class KeyAuthenticator implements AuthenticatorInterface
 {
-    /** @var string */
-    protected $key;
+    protected string $key;
 
-    public function __construct($key)
+    public function __construct(string $key)
     {
         $this->key = $key;
     }
 
-    public function isAuthorized(RequestInterface $request)
+    public function isAuthorized(RequestInterface $request): bool
     {
         parse_str($request->getUri()->getQuery(), $arguments);
+        $sentKey = null;
         if (!isset($arguments['Key']) || (!empty($this->key) && empty($sentKey = $arguments['Key']))) {
             return false;
         }
 
-        $shortenedTimestamp = substr(time(), 0, 7);
+        $shortenedTimestamp = substr((string)time(), 0, 7);
         $hash = hash_hmac('sha256', utf8_encode($this->key), utf8_encode($shortenedTimestamp));
         $encodedHash = base64_encode($hash);
         $calculatedKey = str_replace(['=', '/', '+'], '', $encodedHash);
diff --git a/tests/Exception/NotImplementedExceptionTest.php b/tests/Exception/NotImplementedExceptionTest.php
index 00396fc..dcac194 100644
--- a/tests/Exception/NotImplementedExceptionTest.php
+++ b/tests/Exception/NotImplementedExceptionTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -18,7 +18,7 @@
 class NotImplementedExceptionTest extends TestCase
 {
     /** @throws NotImplementedException */
-    public function testMessage()
+    public function testMessage(): void
     {
         $this->expectException(NotImplementedException::class);
         $this->expectExceptionMessage('Diese Aktion ist nicht implementiert');
diff --git a/tests/Http/MessageTraitTest.php b/tests/Http/MessageTraitTest.php
index a2691da..71a0c6a 100644
--- a/tests/Http/MessageTraitTest.php
+++ b/tests/Http/MessageTraitTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -15,27 +15,31 @@
 use Billbee\CustomShopApi\Http\Message;
 use MintWare\Streams\MemoryStream;
 use PHPUnit\Framework\TestCase;
+use Psr\Http\Message\RequestInterface;
 
 class MessageTraitTest extends TestCase
 {
-    public function testConstructor()
+    public function testConstructor(): void
     {
+        /** @var Message<RequestInterface> $mock */
         $mock = $this->getMockForAbstractClass(Message::class);
 
         $this->assertSame('1.1', $mock->getProtocolVersion());
         $this->assertSame([], $mock->getHeaders());
-        $this->assertNull($mock->getBody());
+        $this->assertNotNull($mock->getBody());
     }
 
-    public function testWithProtocolVersion()
+    public function testWithProtocolVersion(): void
     {
+        /** @var Message<RequestInterface> $mock */
         $mock = $this->getMockForAbstractClass(Message::class);
         $newTrait = $mock->withProtocolVersion('1.2');
         $this->assertEquals('1.2', $newTrait->getProtocolVersion());
     }
 
-    public function testHeaders()
+    public function testHeaders(): void
     {
+        /** @var Message<RequestInterface> $mock */
         $mock = $this->getMockForAbstractClass(Message::class);
         $this->assertFalse($mock->hasHeader('foo'));
         $this->assertEmpty($mock->getHeaders());
@@ -60,8 +64,9 @@ public function testHeaders()
         $this->assertTrue($newTrait->hasHeader('baz'));
     }
 
-    public function testWithBody()
+    public function testWithBody(): void
     {
+        /** @var Message<RequestInterface> $mock */
         $mock = $this->getMockForAbstractClass(Message::class);
         $streamMock = $this->createMock(MemoryStream::class);
 
diff --git a/tests/Http/RequestHandlerPoolTest.php b/tests/Http/RequestHandlerPoolTest.php
index 3d7fdcc..c4c4e39 100644
--- a/tests/Http/RequestHandlerPoolTest.php
+++ b/tests/Http/RequestHandlerPoolTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -28,7 +28,7 @@
 
 class RequestHandlerPoolTest extends TestCase
 {
-    public function testConstructorSimple()
+    public function testConstructorSimple(): void
     {
         $orderRepoMock = $this->createMock(OrdersRepositoryInterface::class);
         $rhp = new RequestHandlerPool(null, [$orderRepoMock]);
@@ -39,7 +39,7 @@ public function testConstructorSimple()
         $this->assertNull($rhp->getAuthenticator());
     }
 
-    public function testConstructorAdvanced()
+    public function testConstructorAdvanced(): void
     {
         $authMock = $this->createMock(AuthenticatorInterface::class);
         $orderRepoMock = $this->createMock(OrdersRepositoryInterface::class);
@@ -56,11 +56,11 @@ public function testConstructorAdvanced()
         $this->assertEquals($authMock, $rhp->getAuthenticator());
     }
 
-    public function testHandleFailsUnauthorized()
+    public function testHandleFailsUnauthorized(): void
     {
         $authMock = $this->createMock(AuthenticatorInterface::class);
         $authMock->method('isAuthorized')
-                 ->willReturn(false);
+            ->willReturn(false);
 
         $orderRepoMock = $this->createMock(OrdersRepositoryInterface::class);
         $rhp = new RequestHandlerPool($authMock, [$orderRepoMock]);
@@ -73,11 +73,11 @@ public function testHandleFailsUnauthorized()
         $this->assertEquals('Unautorisiert', (string)$response->getBody());
     }
 
-    public function testHandleFailsNoAction()
+    public function testHandleFailsNoAction(): void
     {
         $authMock = $this->createMock(AuthenticatorInterface::class);
         $authMock->method('isAuthorized')
-                 ->willReturn(true);
+            ->willReturn(true);
 
         $orderRepoMock = $this->createMock(OrdersRepositoryInterface::class);
         $rhp = new RequestHandlerPool($authMock, [$orderRepoMock]);
@@ -90,11 +90,11 @@ public function testHandleFailsNoAction()
         $this->assertEquals('Keine Aktion übergeben.', (string)$response->getBody());
     }
 
-    public function testHandleFailsNotImplementedAction()
+    public function testHandleFailsNotImplementedAction(): void
     {
         $authMock = $this->createMock(AuthenticatorInterface::class);
         $authMock->method('isAuthorized')
-                 ->willReturn(true);
+            ->willReturn(true);
 
         $orderRepoMock = $this->createMock(OrdersRepositoryInterface::class);
         $rhp = new RequestHandlerPool($authMock, [$orderRepoMock]);
@@ -107,15 +107,15 @@ public function testHandleFailsNotImplementedAction()
         $this->assertEquals('Diese Aktion ist nicht implementiert.', (string)$response->getBody());
     }
 
-    public function testHandle()
+    public function testHandle(): void
     {
         $authMock = $this->createMock(AuthenticatorInterface::class);
         $authMock->method('isAuthorized')
-                 ->willReturn(true);
+            ->willReturn(true);
 
         $orderRepoMock = $this->createMock(OrdersRepositoryInterface::class);
         $orderRepoMock->method('getOrder')
-                      ->willReturn(new Order());
+            ->willReturn(new Order());
 
         $rhp = new RequestHandlerPool($authMock, [$orderRepoMock]);
 
diff --git a/tests/Http/RequestTest.php b/tests/Http/RequestTest.php
index 8a86d47..455e16b 100644
--- a/tests/Http/RequestTest.php
+++ b/tests/Http/RequestTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -19,13 +19,13 @@
 
 class RequestTest extends TestCase
 {
-    public function testConstructor()
+    public function testConstructor(): void
     {
         $request = new Request();
         $this->assertInstanceOf(RequestInterface::class, $request);
     }
 
-    public function testCreateFromGlobals()
+    public function testCreateFromGlobals(): void
     {
         $_SERVER['SERVER_PROTOCOL'] = 'HTTP/1.2';
         $_SERVER['HTTPS'] = 1;
@@ -42,21 +42,21 @@ public function testCreateFromGlobals()
         $this->assertSame('/index.php', $request->getRequestTarget());
     }
 
-    public function testWithRequestTarget()
+    public function testWithRequestTarget(): void
     {
         $request = new Request();
         $newRequest = $request->withRequestTarget('/foo.php');
         $this->assertSame('/foo.php', $newRequest->getRequestTarget());
     }
 
-    public function testWithMethod()
+    public function testWithMethod(): void
     {
         $request = new Request();
         $newRequest = $request->withMethod('DELETE');
         $this->assertSame('DELETE', $newRequest->getMethod());
     }
 
-    public function testWithUri()
+    public function testWithUri(): void
     {
         $request = new Request();
 
diff --git a/tests/Http/ResponseTest.php b/tests/Http/ResponseTest.php
index 157abdf..64578c3 100644
--- a/tests/Http/ResponseTest.php
+++ b/tests/Http/ResponseTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -19,7 +19,7 @@
 
 class ResponseTest extends TestCase
 {
-    public function testConstructor()
+    public function testConstructor(): void
     {
         $response = new Response('{}', 201, 'Created', ['Cookie' => ['1234']], '1.2');
         $this->assertInstanceOf(ResponseInterface::class, $response);
@@ -31,86 +31,86 @@ public function testConstructor()
         $this->assertEquals('1.2', $response->getProtocolVersion());
     }
 
-    public function testConstructorWithStreamInterface()
+    public function testConstructorWithStreamInterface(): void
     {
         $stream = $this->createMock(StreamInterface::class);
         $stream->method('__toString')
-               ->willReturn('Hello World');
+            ->willReturn('Hello World');
 
         $response = new Response($stream);
         $this->assertInstanceOf(ResponseInterface::class, $response);
         $this->assertEquals('Hello World', (string)$response->getBody());
     }
 
-    public function testJson()
+    public function testJson(): void
     {
-        $response = Response::json(['a' => 'b'], 201, 'Created', ['foo' => 'bar'], '1.2');
+        $response = Response::json(['a' => 'b'], 201, 'Created', ['foo' => ['bar']], '1.2');
         $this->assertEquals('{"a":"b"}', (string)$response->getBody());
         $this->assertEquals(201, $response->getStatusCode());
         $this->assertEquals('Created', $response->getReasonPhrase());
-        $this->assertEquals(['foo' => 'bar', 'content-type' => ['application/json']], $response->getHeaders());
+        $this->assertEquals(['foo' => ['bar'], 'content-type' => ['application/json']], $response->getHeaders());
         $this->assertEquals('1.2', $response->getProtocolVersion());
     }
 
-    public function testNotFound()
+    public function testNotFound(): void
     {
-        $response = Response::notFound('Error', ['foo' => 'bar'], '1.2');
+        $response = Response::notFound('Error', ['foo' => ['bar']], '1.2');
         $this->assertEquals('Error', (string)$response->getBody());
         $this->assertEquals(404, $response->getStatusCode());
         $this->assertEquals('Not Found', $response->getReasonPhrase());
-        $this->assertEquals(['foo' => 'bar'], $response->getHeaders());
+        $this->assertEquals(['foo' => ['bar']], $response->getHeaders());
         $this->assertEquals('1.2', $response->getProtocolVersion());
     }
 
-    public function testUnauthorized()
+    public function testUnauthorized(): void
     {
-        $response = Response::unauthorized('Error', ['foo' => 'bar'], '1.2');
+        $response = Response::unauthorized('Error', ['foo' => ['bar']], '1.2');
         $this->assertEquals('Error', (string)$response->getBody());
         $this->assertEquals(401, $response->getStatusCode());
         $this->assertEquals('Unauthorized', $response->getReasonPhrase());
-        $this->assertEquals(['foo' => 'bar'], $response->getHeaders());
+        $this->assertEquals(['foo' => ['bar']], $response->getHeaders());
         $this->assertEquals('1.2', $response->getProtocolVersion());
     }
 
-    public function testForbidden()
+    public function testForbidden(): void
     {
-        $response = Response::forbidden('Error', ['foo' => 'bar'], '1.2');
+        $response = Response::forbidden('Error', ['foo' => ['bar']], '1.2');
         $this->assertEquals('Error', (string)$response->getBody());
         $this->assertEquals(403, $response->getStatusCode());
         $this->assertEquals('Forbidden', $response->getReasonPhrase());
-        $this->assertEquals(['foo' => 'bar'], $response->getHeaders());
+        $this->assertEquals(['foo' => ['bar']], $response->getHeaders());
         $this->assertEquals('1.2', $response->getProtocolVersion());
     }
 
-    public function testBadRequest()
+    public function testBadRequest(): void
     {
-        $response = Response::badRequest('Error', ['foo' => 'bar'], '1.2');
+        $response = Response::badRequest('Error', ['foo' => ['bar']], '1.2');
         $this->assertEquals('Error', (string)$response->getBody());
         $this->assertEquals(400, $response->getStatusCode());
         $this->assertEquals('Bad Request', $response->getReasonPhrase());
-        $this->assertEquals(['foo' => 'bar'], $response->getHeaders());
+        $this->assertEquals(['foo' => ['bar']], $response->getHeaders());
         $this->assertEquals('1.2', $response->getProtocolVersion());
     }
 
-    public function testInternalServerError()
+    public function testInternalServerError(): void
     {
-        $response = Response::internalServerError('Error', ['foo' => 'bar'], '1.2');
+        $response = Response::internalServerError('Error', ['foo' => ['bar']], '1.2');
         $this->assertEquals('Error', (string)$response->getBody());
         $this->assertEquals(500, $response->getStatusCode());
         $this->assertEquals('Internal Server Error', $response->getReasonPhrase());
-        $this->assertEquals(['foo' => 'bar'], $response->getHeaders());
+        $this->assertEquals(['foo' => ['bar']], $response->getHeaders());
         $this->assertEquals('1.2', $response->getProtocolVersion());
     }
 
     /**
      * @runInSeparateProcess
      */
-    public function testSend()
+    public function testSend(): void
     {
         $this->assertEquals(1, ob_get_level());
 
         ob_start();
-        $response = Response::unauthorized('Unauthorized', ['foo' => 'bar']);
+        $response = Response::unauthorized('Unauthorized', ['foo' => ['bar']]);
         $response->send(false);
         $contents = ob_get_contents();
         ob_end_clean();
@@ -119,7 +119,7 @@ public function testSend()
         $this->assertEquals(['foo: bar', 'content-length: 12'], xdebug_get_headers());
     }
 
-    public function testWithStatus()
+    public function testWithStatus(): void
     {
         $response = new Response();
         $this->assertEquals(200, $response->getStatusCode());
diff --git a/tests/Http/UriTest.php b/tests/Http/UriTest.php
index 8be76b8..a4d2fab 100644
--- a/tests/Http/UriTest.php
+++ b/tests/Http/UriTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -18,7 +18,7 @@
 
 class UriTest extends TestCase
 {
-    public function testConstructor()
+    public function testConstructor(): void
     {
         $uri = new Uri('https://user:password@php.unit.tld:01337/file.php?param1=foo&param2=bar#fragment');
         $this->assertInstanceOf(UriInterface::class, $uri);
@@ -31,10 +31,13 @@ public function testConstructor()
         $this->assertEquals('param1=foo&param2=bar', $uri->getQuery());
         $this->assertEquals('fragment', $uri->getFragment());
         $this->assertEquals('user:password@php.unit.tld:1337', $uri->getAuthority());
-        $this->assertEquals('https://user:password@php.unit.tld:1337/file.php?param1=foo&param2=bar#fragment', (string)$uri);
+        $this->assertEquals(
+            'https://user:password@php.unit.tld:1337/file.php?param1=foo&param2=bar#fragment',
+            (string)$uri
+        );
     }
 
-    public function testWithScheme()
+    public function testWithScheme(): void
     {
         $uri = new Uri('https://php.unit.tld');
         $this->assertEquals('https', $uri->getScheme());
@@ -43,7 +46,7 @@ public function testWithScheme()
         $this->assertEquals('http', $newUri->getScheme());
     }
 
-    public function testUserInfo()
+    public function testUserInfo(): void
     {
         $uri = new Uri('https://php.unit.tld');
         $this->assertEquals('', $uri->getUserInfo());
@@ -52,7 +55,7 @@ public function testUserInfo()
         $this->assertEquals('user:password', $newUri->getUserInfo());
     }
 
-    public function testWithHost()
+    public function testWithHost(): void
     {
         $uri = new Uri('https://php.unit.tld');
         $this->assertEquals('php.unit.tld', $uri->getHost());
@@ -61,16 +64,16 @@ public function testWithHost()
         $this->assertEquals('another.host.tld', $newUri->getHost());
     }
 
-    public function testWithPort()
+    public function testWithPort(): void
     {
         $uri = new Uri('https://php.unit.tld');
         $this->assertEquals('', $uri->getPort());
-        $newUri = $uri->withPort('01337');
+        $newUri = $uri->withPort(1337);
         $this->assertEquals('', $uri->getPort());
         $this->assertEquals(1337, $newUri->getPort());
     }
 
-    public function testWithPath()
+    public function testWithPath(): void
     {
         $uri = new Uri('https://php.unit.tld');
         $this->assertEquals('', $uri->getPath());
@@ -79,7 +82,7 @@ public function testWithPath()
         $this->assertEquals('/another.file.php', $newUri->getPath());
     }
 
-    public function testWithQuery()
+    public function testWithQuery(): void
     {
         $uri = new Uri('https://php.unit.tld');
         $this->assertEquals('', $uri->getQuery());
@@ -88,7 +91,7 @@ public function testWithQuery()
         $this->assertEquals('param1=foo&param2=bar', $newUri->getQuery());
     }
 
-    public function testWithFragment()
+    public function testWithFragment(): void
     {
         $uri = new Uri('https://php.unit.tld');
         $this->assertEquals('', $uri->getFragment());
diff --git a/tests/Model/AddressTest.php b/tests/Model/AddressTest.php
index 7654775..f93044a 100644
--- a/tests/Model/AddressTest.php
+++ b/tests/Model/AddressTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -10,14 +10,14 @@
  * Created by Julian Finkler <julian@mintware.de>
  */
 
-namespace Billbee\Tests\CustomShopApi\Model\Response;
+namespace Billbee\Tests\CustomShopApi\Model;
 
 use Billbee\CustomShopApi\Model\Address;
 use PHPUnit\Framework\TestCase;
 
 class AddressTest extends TestCase
 {
-    public function testGettersSetters()
+    public function testGettersSetters(): void
     {
         $address = new Address();
         $this->assertNull($address->getFirstName());
@@ -32,15 +32,15 @@ public function testGettersSetters()
         $this->assertNull($address->getState());
 
         $address->setFirstName('FirstName')
-                ->setLastName('LastName')
-                ->setStreet('Street')
-                ->setHouseNumber('HouseNumber')
-                ->setAddress2('Address2')
-                ->setPostcode('Postcode')
-                ->setCity('City')
-                ->setCountryCode('CountryCode')
-                ->setCompany('Company')
-                ->setState('State');
+            ->setLastName('LastName')
+            ->setStreet('Street')
+            ->setHouseNumber('HouseNumber')
+            ->setAddress2('Address2')
+            ->setPostcode('Postcode')
+            ->setCity('City')
+            ->setCountryCode('CountryCode')
+            ->setCompany('Company')
+            ->setState('State');
 
         $this->assertEquals('FirstName', $address->getFirstName());
         $this->assertEquals('LastName', $address->getLastName());
diff --git a/tests/Model/OrderCommentTest.php b/tests/Model/OrderCommentTest.php
index 62ea954..295f9ae 100644
--- a/tests/Model/OrderCommentTest.php
+++ b/tests/Model/OrderCommentTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -18,7 +18,7 @@
 
 class OrderCommentTest extends TestCase
 {
-    public function testGettersSetters()
+    public function testGettersSetters():void
     {
         $comment = new OrderComment();
         $this->assertNull($comment->getDateAdded());
diff --git a/tests/Model/OrderProductOptionTest.php b/tests/Model/OrderProductOptionTest.php
index 5c0026e..363ef18 100644
--- a/tests/Model/OrderProductOptionTest.php
+++ b/tests/Model/OrderProductOptionTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -17,14 +17,14 @@
 
 class OrderProductOptionTest extends TestCase
 {
-    public function testConstructor()
+    public function testConstructor():void
     {
         $productOption = new OrderProductOption('color', 'red');
         $this->assertEquals('color', $productOption->getName());
         $this->assertEquals('red', $productOption->getValue());
     }
 
-    public function testGettersSetters()
+    public function testGettersSetters():void
     {
         $productOption = new OrderProductOption();
 
diff --git a/tests/Model/OrderProductTest.php b/tests/Model/OrderProductTest.php
index afb7ab2..47aa0c8 100644
--- a/tests/Model/OrderProductTest.php
+++ b/tests/Model/OrderProductTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -17,7 +17,7 @@
 
 class OrderProductTest extends TestCase
 {
-    public function testGettersSetters()
+    public function testGettersSetters():void
     {
         $product = new OrderProduct();
 
diff --git a/tests/Model/OrderTest.php b/tests/Model/OrderTest.php
index 3024f0a..e011129 100644
--- a/tests/Model/OrderTest.php
+++ b/tests/Model/OrderTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -19,7 +19,7 @@
 
 class OrderTest extends TestCase
 {
-    public function testGettersSetters()
+    public function testGettersSetters(): void
     {
         $order = new Order();
         $this->assertNull($order->getOrderId());
@@ -51,26 +51,26 @@ public function testGettersSetters()
         $shipDate = new DateTime();
 
         $order->setOrderId('1234')
-              ->setOrderNumber('5678')
-              ->setCurrencyCode('EUR')
-              ->setDeliverySourceCountryCode('DE')
-              ->setNickName('foobar')
-              ->setShipCost(3.99)
-              ->setInvoiceAddress($invoiceAddress)
-              ->setDeliveryAddress($deliveryAddress)
-              ->setOrderDate($orderDate)
-              ->setEmail('hello@world.tld')
-              ->setPhone1('PHONE 12345')
-              ->setPayDate($payDate)
-              ->setShipDate($shipDate)
-              ->setPaymentMethod(2)
-              ->setStatusId(1)
-              ->setItems([])
-              ->setComments([])
-              ->setSellerComment('Seller Comment')
-              ->setShippingProfileId('FLATRATE')
-              ->setVatId('DE1234')
-              ->setPaymentTransactionId('PAY-1234');
+            ->setOrderNumber('5678')
+            ->setCurrencyCode('EUR')
+            ->setDeliverySourceCountryCode('DE')
+            ->setNickName('foobar')
+            ->setShipCost(3.99)
+            ->setInvoiceAddress($invoiceAddress)
+            ->setDeliveryAddress($deliveryAddress)
+            ->setOrderDate($orderDate)
+            ->setEmail('hello@world.tld')
+            ->setPhone1('PHONE 12345')
+            ->setPayDate($payDate)
+            ->setShipDate($shipDate)
+            ->setPaymentMethod(2)
+            ->setStatusId(1)
+            ->setItems([])
+            ->setComments([])
+            ->setSellerComment('Seller Comment')
+            ->setShippingProfileId('FLATRATE')
+            ->setVatId('DE1234')
+            ->setPaymentTransactionId('PAY-1234');
 
         $this->assertEquals('1234', $order->getOrderId());
         $this->assertEquals('5678', $order->getOrderNumber());
diff --git a/tests/Model/PagedDataTest.php b/tests/Model/PagedDataTest.php
index 0ea24c0..8b0489d 100644
--- a/tests/Model/PagedDataTest.php
+++ b/tests/Model/PagedDataTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -18,14 +18,14 @@
 
 class PagedDataTest extends TestCase
 {
-    public function testConstructorFailsInvalidCount()
+    public function testConstructorFailsInvalidCount(): void
     {
         $this->expectException(RuntimeException::class);
         $this->expectExceptionMessage('totalCount must be greater or equal as the count of data.');
         new PagedData([1], 0);
     }
 
-    public function testConstructor()
+    public function testConstructor(): void
     {
         $pagedData = new PagedData([1], 2);
         $this->assertEquals(2, $pagedData->getTotalCount());
diff --git a/tests/Model/PaginationTest.php b/tests/Model/PaginationTest.php
index 19a7646..a08d2db 100644
--- a/tests/Model/PaginationTest.php
+++ b/tests/Model/PaginationTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -17,7 +17,7 @@
 
 class PaginationTest extends TestCase
 {
-    public function testConstructorSimple()
+    public function testConstructorSimple(): void
     {
         $pagination = new Pagination();
         $this->assertEquals(1, $pagination->getPage());
@@ -25,7 +25,7 @@ public function testConstructorSimple()
         $this->assertEquals(0, $pagination->getTotalPages());
     }
 
-    public function testConstructorAdvance()
+    public function testConstructorAdvance(): void
     {
         $pagination = new Pagination(1, 50, 100);
         $this->assertEquals(1, $pagination->getPage());
diff --git a/tests/Model/ProductImageTest.php b/tests/Model/ProductImageTest.php
index a8af22c..d8fbeb7 100644
--- a/tests/Model/ProductImageTest.php
+++ b/tests/Model/ProductImageTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -17,7 +17,7 @@
 
 class ProductImageTest extends TestCase
 {
-    public function testGettersSetters()
+    public function testGettersSetters(): void
     {
         $image = new ProductImage();
         $this->assertNull($image->getUrl());
@@ -26,7 +26,7 @@ public function testGettersSetters()
 
         $image->setUrl('http://domain.tld/image.jpeg');
         $image->setIsDefault(true);
-        $image->setPosition('3');
+        $image->setPosition(3);
 
         $this->assertSame('http://domain.tld/image.jpeg', $image->getUrl());
         $this->assertTrue($image->isDefault());
diff --git a/tests/Model/ProductTest.php b/tests/Model/ProductTest.php
index eb1db9c..4f26e20 100644
--- a/tests/Model/ProductTest.php
+++ b/tests/Model/ProductTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -17,7 +17,7 @@
 
 class ProductTest extends TestCase
 {
-    public function testGettersSetters()
+    public function testGettersSetters():void
     {
         $product = new Product();
         $this->assertNull($product->getMaterial());
diff --git a/tests/Model/Response/GetOrdersResponseTest.php b/tests/Model/Response/GetOrdersResponseTest.php
index 5c4938a..b2a55ce 100644
--- a/tests/Model/Response/GetOrdersResponseTest.php
+++ b/tests/Model/Response/GetOrdersResponseTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -18,7 +18,7 @@
 
 class GetOrdersResponseTest extends TestCase
 {
-    public function testConstructor()
+    public function testConstructor():void
     {
         $paging = new Pagination(1, 1, 1);
         $resp = new GetOrdersResponse($paging, []);
diff --git a/tests/Model/Response/GetProductsResponseTest.php b/tests/Model/Response/GetProductsResponseTest.php
index 97dc0bd..89e0239 100644
--- a/tests/Model/Response/GetProductsResponseTest.php
+++ b/tests/Model/Response/GetProductsResponseTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -18,7 +18,7 @@
 
 class GetProductsResponseTest extends TestCase
 {
-    public function testConstructor()
+    public function testConstructor(): void
     {
         $paging = new Pagination(1, 1, 1);
         $resp = new GetProductsResponse($paging, []);
diff --git a/tests/Model/ShippingProfileTest.php b/tests/Model/ShippingProfileTest.php
index 3f15c3c..ad5d039 100644
--- a/tests/Model/ShippingProfileTest.php
+++ b/tests/Model/ShippingProfileTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -17,28 +17,28 @@
 
 class ShippingProfileTest extends TestCase
 {
-    public function testConstructorSimple()
+    public function testConstructorSimple(): void
     {
         $profile = new ShippingProfile();
         $this->assertNull($profile->getId());
         $this->assertNull($profile->getName());
     }
 
-    public function testConstructorAdvanced()
+    public function testConstructorAdvanced(): void
     {
         $profile = new ShippingProfile('Shipper2', 'Shipper 2');
         $this->assertEquals($profile->getId(), 'Shipper2');
         $this->assertEquals($profile->getName(), 'Shipper 2');
     }
 
-    public function testGettersSetters()
+    public function testGettersSetters(): void
     {
         $profile = new ShippingProfile();
         $this->assertNull($profile->getId());
         $this->assertNull($profile->getName());
 
         $profile->setId('shipper1')
-                ->setName('Shipper 1');
+            ->setName('Shipper 1');
         $this->assertEquals('shipper1', $profile->getId());
         $this->assertEquals('Shipper 1', $profile->getName());
     }
diff --git a/tests/RequestHandler/OrderRequestHandlerTest.php b/tests/RequestHandler/OrderRequestHandlerTest.php
index 816296a..d870ff7 100644
--- a/tests/RequestHandler/OrderRequestHandlerTest.php
+++ b/tests/RequestHandler/OrderRequestHandlerTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -29,7 +29,7 @@
 
 class OrderRequestHandlerTest extends TestCase
 {
-    public function testConstructor()
+    public function testConstructor(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
 
@@ -42,11 +42,11 @@ public function testConstructor()
         }
     }
 
-    public function testGetOrders()
+    public function testGetOrders(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
         $repo->method('getOrders')
-             ->willReturn(new PagedData([$this->createDemoOrder()], 1));
+            ->willReturn(new PagedData([$this->createDemoOrder()], 1));
         $handler = new OrderRequestHandler($repo);
 
         $request = new Request();
@@ -56,7 +56,8 @@ public function testGetOrders()
         parse_str($uri->getQuery(), $arguments);
 
         $response = $handler->handle($req, $arguments);
-        $data = json_decode($response->getBody(), true);
+        /** @var array{"paging": array{"page": int, "totalPages": int, "totalCount": int}} $data */
+        $data = json_decode((string)$response->getBody(), true);
 
         $this->assertEquals(200, $response->getStatusCode());
         $this->assertEquals(1, $data['paging']['page']);
@@ -66,11 +67,11 @@ public function testGetOrders()
         $this->assertEquals($body, (string)$response->getBody());
     }
 
-    public function testGetOrdersFailsInvalidDAte()
+    public function testGetOrdersFailsInvalidDAte(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
         $repo->method('getOrders')
-             ->willReturn(new PagedData([$this->createDemoOrder()], 1));
+            ->willReturn(new PagedData([$this->createDemoOrder()], 1));
         $handler = new OrderRequestHandler($repo);
 
         $request = new Request();
@@ -79,10 +80,13 @@ public function testGetOrdersFailsInvalidDAte()
 
         $response = $handler->handle($req, ['Action' => 'GetOrders', 'StartDate' => 'Hallo Welt']);
         $this->assertEquals(500, $response->getStatusCode());
-        $this->assertEquals('Der Wert Hallo Welt konnte nicht in eine gültiges Datum umgewandelt werden.', (string)$response->getBody());
+        $this->assertEquals(
+            'Der Wert Hallo Welt konnte nicht in eine gültiges Datum umgewandelt werden.',
+            (string)$response->getBody()
+        );
     }
 
-    public function testAckOrderFailsNoOrderId()
+    public function testAckOrderFailsNoOrderId(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
         $handler = new OrderRequestHandler($repo);
@@ -97,18 +101,18 @@ public function testAckOrderFailsNoOrderId()
         $this->assertEquals('Es wurde keine OrderId übergeben', (string)$response->getBody());
     }
 
-    public function testAckOrderFailsNotFound()
+    public function testAckOrderFailsNotFound(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
         $repo->method('acknowledgeOrder')
-             ->willThrowException(new OrderNotFoundException());
+            ->willThrowException(new OrderNotFoundException());
         $handler = new OrderRequestHandler($repo);
 
         /** @var RequestInterface $request */
         $request = new Request();
         $uri = new Uri('http://localhost/?Action=AckOrder');
         $req = $request->withUri($uri)
-                       ->withBody(new MemoryStream(http_build_query(['OrderId' => '1'])));
+            ->withBody(new MemoryStream(http_build_query(['OrderId' => '1'])));
 
         $response = $handler->handle($req, ['Action' => 'AckOrder']);
 
@@ -116,18 +120,18 @@ public function testAckOrderFailsNotFound()
         $this->assertEquals('Die Bestellung wurde nicht gefunden', (string)$response->getBody());
     }
 
-    public function testAckOrderFailsUnknownError()
+    public function testAckOrderFailsUnknownError(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
         $repo->method('acknowledgeOrder')
-             ->willThrowException(new Exception('Unknown Error'));
+            ->willThrowException(new Exception('Unknown Error'));
         $handler = new OrderRequestHandler($repo);
 
         /** @var RequestInterface $request */
         $request = new Request();
         $uri = new Uri('http://localhost/?Action=AckOrder&OrderId=1');
         $req = $request->withUri($uri)
-                       ->withBody(new MemoryStream(http_build_query(['OrderId' => '1'])));
+            ->withBody(new MemoryStream(http_build_query(['OrderId' => '1'])));
 
 
         $response = $handler->handle($req, ['Action' => 'AckOrder']);
@@ -136,18 +140,18 @@ public function testAckOrderFailsUnknownError()
         $this->assertEquals('Unknown Error', (string)$response->getBody());
     }
 
-    public function testAckOrder()
+    public function testAckOrder(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
         $repo->method('acknowledgeOrder')
-             ->willReturn(null);
+            ->willReturn(null);
         $handler = new OrderRequestHandler($repo);
 
         /** @var RequestInterface $request */
         $request = new Request();
         $uri = new Uri('http://localhost/?Action=AckOrder&OrderId=1');
         $req = $request->withUri($uri)
-                       ->withBody(new MemoryStream(http_build_query(['OrderId' => '1'])));
+            ->withBody(new MemoryStream(http_build_query(['OrderId' => '1'])));
 
 
         $response = $handler->handle($req, ['Action' => 'AckOrder']);
@@ -155,7 +159,7 @@ public function testAckOrder()
         $this->assertEquals(200, $response->getStatusCode());
     }
 
-    public function testGetOrderFailsNoOrderId()
+    public function testGetOrderFailsNoOrderId(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
         $handler = new OrderRequestHandler($repo);
@@ -170,11 +174,11 @@ public function testGetOrderFailsNoOrderId()
         $this->assertEquals('Es wurde keine OrderId übergeben', (string)$response->getBody());
     }
 
-    public function testGetOrderFailsNotFound()
+    public function testGetOrderFailsNotFound(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
         $repo->method('getOrder')
-             ->willThrowException(new OrderNotFoundException());
+            ->willThrowException(new OrderNotFoundException());
         $handler = new OrderRequestHandler($repo);
 
         $request = new Request();
@@ -187,11 +191,11 @@ public function testGetOrderFailsNotFound()
         $this->assertEquals('Die Bestellung wurde nicht gefunden', (string)$response->getBody());
     }
 
-    public function testGetOrderFailsUnknownError()
+    public function testGetOrderFailsUnknownError(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
         $repo->method('getOrder')
-             ->willThrowException(new Exception('Unknown Error'));
+            ->willThrowException(new Exception('Unknown Error'));
         $handler = new OrderRequestHandler($repo);
 
         $request = new Request();
@@ -204,11 +208,11 @@ public function testGetOrderFailsUnknownError()
         $this->assertEquals('Unknown Error', (string)$response->getBody());
     }
 
-    public function testGetOrder()
+    public function testGetOrder(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
         $repo->method('getOrder')
-             ->willReturn($this->createDemoOrder());
+            ->willReturn($this->createDemoOrder());
 
         $handler = new OrderRequestHandler($repo);
 
@@ -223,7 +227,7 @@ public function testGetOrder()
         $this->assertEquals($bodyJson, (string)$response->getBody());
     }
 
-    public function testSetOrderStateFailsNoOrderId()
+    public function testSetOrderStateFailsNoOrderId(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
         $handler = new OrderRequestHandler($repo);
@@ -238,7 +242,7 @@ public function testSetOrderStateFailsNoOrderId()
         $this->assertEquals('Es wurde keine OrderId übergeben', (string)$response->getBody());
     }
 
-    public function testSetOrderStateFailsNoNewStateTypeId()
+    public function testSetOrderStateFailsNoNewStateTypeId(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
         $handler = new OrderRequestHandler($repo);
@@ -254,17 +258,19 @@ public function testSetOrderStateFailsNoNewStateTypeId()
         $this->assertEquals('Es wurde keine NewStateTypeId übergeben', (string)$response->getBody());
     }
 
-    public function testSetOrderStateFailsNotFound()
+    public function testSetOrderStateFailsNotFound(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
         $repo->method('setOrderState')
-             ->willThrowException(new OrderNotFoundException());
+            ->willThrowException(new OrderNotFoundException());
         $handler = new OrderRequestHandler($repo);
 
         /** @var RequestInterface $request */
         $request = new Request();
         $uri = new Uri('http://localhost/?Action=SetOrderState');
-        $req = $request->withUri($uri)->withBody(new MemoryStream(http_build_query(['OrderId' => 1, 'NewStateTypeId' => 1])));
+        $req = $request->withUri($uri)->withBody(
+            new MemoryStream(http_build_query(['OrderId' => 1, 'NewStateTypeId' => 1]))
+        );
 
         $response = $handler->handle($req, ['Action' => 'SetOrderState']);
 
@@ -272,17 +278,19 @@ public function testSetOrderStateFailsNotFound()
         $this->assertEquals('Die Bestellung wurde nicht gefunden', (string)$response->getBody());
     }
 
-    public function testSetOrderStateUnknownError()
+    public function testSetOrderStateUnknownError(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
         $repo->method('setOrderState')
-             ->willThrowException(new Exception('Unknown Error'));
+            ->willThrowException(new Exception('Unknown Error'));
         $handler = new OrderRequestHandler($repo);
 
         /** @var RequestInterface $request */
         $request = new Request();
         $uri = new Uri('http://localhost/?Action=SetOrderState');
-        $req = $request->withUri($uri)->withBody(new MemoryStream(http_build_query(['OrderId' => 1, 'NewStateTypeId' => 1])));
+        $req = $request->withUri($uri)->withBody(
+            new MemoryStream(http_build_query(['OrderId' => 1, 'NewStateTypeId' => 1]))
+        );
 
         $response = $handler->handle($req, ['Action' => 'SetOrderState', 'OrderId' => '1']);
 
@@ -290,32 +298,34 @@ public function testSetOrderStateUnknownError()
         $this->assertEquals('Unknown Error', (string)$response->getBody());
     }
 
-    public function testSetOrderState()
+    public function testSetOrderState(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
         $repo->method('setOrderState')
-             ->willReturn(true);
+            ->willReturn(true);
         $handler = new OrderRequestHandler($repo);
 
         /** @var RequestInterface $request */
         $request = new Request();
         $uri = new Uri('http://localhost/?Action=SetOrderState');
-        $req = $request->withUri($uri)->withBody(new MemoryStream(http_build_query(['OrderId' => 1, 'NewStateTypeId' => 1])));
+        $req = $request->withUri($uri)->withBody(
+            new MemoryStream(http_build_query(['OrderId' => 1, 'NewStateTypeId' => 1]))
+        );
 
         $response = $handler->handle($req, ['Action' => 'SetOrderState', 'OrderId' => '1']);
 
         $this->assertEquals(200, $response->getStatusCode());
     }
 
-    public function testHandleNonExistent()
+    public function testHandleNonExistent(): void
     {
         $repo = $this->createMock(OrdersRepositoryInterface::class);
         $handler = new OrderRequestHandler($repo);
         $response = $handler->handle(new Request(), ['Action' => 'asdf']);
-        $this->assertNull($response);
+        $this->assertEquals(400, $response->getStatusCode());
     }
 
-    private function createDemoOrder()
+    private function createDemoOrder(): Order
     {
         $address = (new Address())
             ->setFirstName('Kara')
diff --git a/tests/RequestHandler/ProductRequestHandlerTest.php b/tests/RequestHandler/ProductRequestHandlerTest.php
index 18a7a10..17f78d3 100644
--- a/tests/RequestHandler/ProductRequestHandlerTest.php
+++ b/tests/RequestHandler/ProductRequestHandlerTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -26,7 +26,7 @@
 
 class ProductRequestHandlerTest extends TestCase
 {
-    public function testConstructor()
+    public function testConstructor(): void
     {
         $repo = $this->createMock(ProductsRepositoryInterface::class);
 
@@ -39,15 +39,15 @@ public function testConstructor()
         }
     }
 
-    public function testHandleNonExistent()
+    public function testHandleNonExistent(): void
     {
         $repo = $this->createMock(ProductsRepositoryInterface::class);
         $handler = new ProductRequestHandler($repo);
         $response = $handler->handle(new Request(), ['Action' => 'asdf']);
-        $this->assertNull($response);
+        $this->assertEquals(400, $response->getStatusCode());
     }
 
-    public function testGetProductFailsNoProductId()
+    public function testGetProductFailsNoProductId(): void
     {
         $repo = $this->createMock(ProductsRepositoryInterface::class);
         $handler = new ProductRequestHandler($repo);
@@ -60,11 +60,11 @@ public function testGetProductFailsNoProductId()
         $this->assertEquals('Es wurde keine ProductId übergeben', (string)$response->getBody());
     }
 
-    public function testGetProductFailsProductNotFound()
+    public function testGetProductFailsProductNotFound(): void
     {
         $repo = $this->createMock(ProductsRepositoryInterface::class);
         $repo->method('getProduct')
-             ->willThrowException(new ProductNotFoundException());
+            ->willThrowException(new ProductNotFoundException());
 
         $handler = new ProductRequestHandler($repo);
         $request = new Request();
@@ -76,11 +76,11 @@ public function testGetProductFailsProductNotFound()
         $this->assertEquals('Der Artikel wurde nicht gefunden', (string)$response->getBody());
     }
 
-    public function testGetProductFailsException()
+    public function testGetProductFailsException(): void
     {
         $repo = $this->createMock(ProductsRepositoryInterface::class);
         $repo->method('getProduct')
-             ->willThrowException(new RuntimeException("Unknown Error"));
+            ->willThrowException(new RuntimeException("Unknown Error"));
 
         $handler = new ProductRequestHandler($repo);
         $request = new Request();
@@ -92,11 +92,11 @@ public function testGetProductFailsException()
         $this->assertEquals('Unknown Error', (string)$response->getBody());
     }
 
-    public function testGetProduct()
+    public function testGetProduct(): void
     {
         $repo = $this->createMock(ProductsRepositoryInterface::class);
         $repo->method('getProduct')
-             ->willReturn($this->createDemoProduct());
+            ->willReturn($this->createDemoProduct());
 
         $handler = new ProductRequestHandler($repo);
         $request = new Request();
@@ -111,11 +111,11 @@ public function testGetProduct()
         );
     }
 
-    public function testGetProductsFailsException()
+    public function testGetProductsFailsException(): void
     {
         $repo = $this->createMock(ProductsRepositoryInterface::class);
         $repo->method('getProducts')
-             ->willThrowException(new RuntimeException("Unknown Error"));
+            ->willThrowException(new RuntimeException("Unknown Error"));
 
         $handler = new ProductRequestHandler($repo);
         $request = new Request();
@@ -127,11 +127,11 @@ public function testGetProductsFailsException()
         $this->assertEquals('Unknown Error', (string)$response->getBody());
     }
 
-    public function testGetProducts()
+    public function testGetProducts(): void
     {
         $repo = $this->createMock(ProductsRepositoryInterface::class);
         $repo->method('getProducts')
-             ->willReturn(new PagedData([$this->createDemoProduct()], 1));
+            ->willReturn(new PagedData([$this->createDemoProduct()], 1));
 
         $handler = new ProductRequestHandler($repo);
         $request = new Request();
@@ -145,7 +145,7 @@ public function testGetProducts()
         $this->assertEquals($json, (string)$response->getBody());
     }
 
-    private function createDemoProduct()
+    private function createDemoProduct(): Product
     {
         return (new Product())
             ->setMaterial('Wood')
diff --git a/tests/RequestHandler/ShippingProfileRequestHandlerTest.php b/tests/RequestHandler/ShippingProfileRequestHandlerTest.php
index 1d62372..695c749 100644
--- a/tests/RequestHandler/ShippingProfileRequestHandlerTest.php
+++ b/tests/RequestHandler/ShippingProfileRequestHandlerTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -22,7 +22,7 @@
 
 class ShippingProfileRequestHandlerTest extends TestCase
 {
-    public function testConstructor()
+    public function testConstructor(): void
     {
         $repo = $this->createMock(ShippingProfileRepositoryInterface::class);
 
@@ -33,20 +33,20 @@ public function testConstructor()
         $this->assertTrue($handler->canHandle($request, ['Action' => 'GetShippingProfiles']));
     }
 
-    public function testHandleNonExistent()
+    public function testHandleNonExistent(): void
     {
         $repo = $this->createMock(ShippingProfileRepositoryInterface::class);
 
         $handler = new ShippingProfileRequestHandler($repo);
         $response = $handler->handle(new Request(), ['Action' => 'asdf']);
-        $this->assertNull($response);
+        $this->assertEquals(400, $response->getStatusCode());
     }
 
-    public function testSetStockFailsException()
+    public function testSetStockFailsException(): void
     {
         $repo = $this->createMock(ShippingProfileRepositoryInterface::class);
         $repo->method('getShippingProfiles')
-             ->willThrowException(new RuntimeException("Unknown Error"));
+            ->willThrowException(new RuntimeException("Unknown Error"));
 
         $handler = new ShippingProfileRequestHandler($repo);
         $request = new Request();
@@ -56,15 +56,16 @@ public function testSetStockFailsException()
         $this->assertEquals('Internal Server Error', $response->getReasonPhrase());
         $this->assertEquals('Unknown Error', (string)$response->getBody());
     }
-    public function testHandle()
+
+    public function testHandle(): void
     {
         $repo = $this->createMock(ShippingProfileRepositoryInterface::class);
 
         $repo->method('getShippingProfiles')
-             ->willReturn([
-                 new ShippingProfile('1', 'Profile 1'),
-                 new ShippingProfile('2', 'Profile 2')
-             ]);
+            ->willReturn([
+                new ShippingProfile('1', 'Profile 1'),
+                new ShippingProfile('2', 'Profile 2')
+            ]);
 
         $handler = new ShippingProfileRequestHandler($repo);
         $response = $handler->handle(new Request(), ['Action' => 'GetShippingProfiles']);
diff --git a/tests/RequestHandler/StockSyncRequestHandlerTest.php b/tests/RequestHandler/StockSyncRequestHandlerTest.php
index a86cd9c..2dff7a9 100644
--- a/tests/RequestHandler/StockSyncRequestHandlerTest.php
+++ b/tests/RequestHandler/StockSyncRequestHandlerTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -23,7 +23,7 @@
 
 class StockSyncRequestHandlerTest extends TestCase
 {
-    public function testConstructor()
+    public function testConstructor(): void
     {
         $repo = $this->createMock(StockSyncRepositoryInterface::class);
 
@@ -34,15 +34,15 @@ public function testConstructor()
         $this->assertTrue($handler->canHandle($request, ['Action' => 'SetStock']));
     }
 
-    public function testHandleNonExistent()
+    public function testHandleNonExistent(): void
     {
         $repo = $this->createMock(StockSyncRepositoryInterface::class);
         $handler = new StockRequestHandler($repo);
         $response = $handler->handle(new Request(), ['Action' => 'asdf']);
-        $this->assertNull($response);
+        $this->assertEquals(400, $response->getStatusCode());
     }
 
-    public function testSetStockFailsNoProductId()
+    public function testSetStockFailsNoProductId(): void
     {
         $repo = $this->createMock(StockSyncRepositoryInterface::class);
         $handler = new StockRequestHandler($repo);
@@ -54,7 +54,7 @@ public function testSetStockFailsNoProductId()
         $this->assertEquals('Es wurde keine ProductId übergeben', (string)$response->getBody());
     }
 
-    public function testSetStockFailsNoAvailableStock()
+    public function testSetStockFailsNoAvailableStock(): void
     {
         $repo = $this->createMock(StockSyncRepositoryInterface::class);
         $handler = new StockRequestHandler($repo);
@@ -67,7 +67,7 @@ public function testSetStockFailsNoAvailableStock()
         $this->assertEquals('Es wurde kein AvailableStock übergeben', (string)$response->getBody());
     }
 
-    public function testSetStockFailsProductNotFound()
+    public function testSetStockFailsProductNotFound(): void
     {
         $repo = $this->createMock(StockSyncRepositoryInterface::class);
         $repo->method('SetStock')
@@ -85,7 +85,7 @@ public function testSetStockFailsProductNotFound()
         $this->assertEquals('Der Artikel wurde nicht gefunden', (string)$response->getBody());
     }
 
-    public function testSetStockFailsException()
+    public function testSetStockFailsException(): void
     {
         $repo = $this->createMock(StockSyncRepositoryInterface::class);
         $repo->method('SetStock')
@@ -93,7 +93,9 @@ public function testSetStockFailsException()
 
         $handler = new StockRequestHandler($repo);
         $request = new Request();
-        $request = $request->withBody(new MemoryStream(http_build_query(['ProductId' => '4177', "AvailableStock" => 123])));
+        $request = $request->withBody(
+            new MemoryStream(http_build_query(['ProductId' => '4177', "AvailableStock" => 123]))
+        );
         $response = $handler->handle($request, ['Action' => 'SetStock']);
 
         $this->assertEquals(500, $response->getStatusCode());
@@ -102,13 +104,15 @@ public function testSetStockFailsException()
     }
 
 
-    public function testSetStock()
+    public function testSetStock(): void
     {
         $repo = $this->createMock(StockSyncRepositoryInterface::class);
 
         $handler = new StockRequestHandler($repo);
         $request = new Request();
-        $request = $request->withBody(new MemoryStream(http_build_query(['ProductId' => '4177', "AvailableStock" => 123])));
+        $request = $request->withBody(
+            new MemoryStream(http_build_query(['ProductId' => '4177', "AvailableStock" => 123]))
+        );
         $response = $handler->handle($request, ['Action' => 'SetStock']);
 
         $this->assertEquals(200, $response->getStatusCode());
diff --git a/tests/Security/KeyAuthenticatorTest.php b/tests/Security/KeyAuthenticatorTest.php
index d6053f9..e646e88 100644
--- a/tests/Security/KeyAuthenticatorTest.php
+++ b/tests/Security/KeyAuthenticatorTest.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.
@@ -20,69 +20,69 @@
 
 class KeyAuthenticatorTest extends TestCase
 {
-    public function testConstructor()
+    public function testConstructor(): void
     {
         $authenticator = new KeyAuthenticator('1234');
         $this->assertInstanceOf(AuthenticatorInterface::class, $authenticator);
         $this->assertEquals('1234', $authenticator->getKey());
     }
 
-    public function testIsAuthorizedNoKey()
+    public function testIsAuthorizedNoKey(): void
     {
         $uriMock = $this->createMock(Uri::class);
         $uriMock->method('getQuery')
-                ->willReturn('');
+            ->willReturn('');
 
         $request = $this->createMock(Request::class);
         $request->method('getUri')
-                ->willReturn($uriMock);
+            ->willReturn($uriMock);
 
         $authenticator = new KeyAuthenticator('1234');
         $this->assertFalse($authenticator->isAuthorized($request));
     }
 
-    public function testIsAuthorizedEmpty()
+    public function testIsAuthorizedEmpty(): void
     {
         $uriMock = $this->createMock(Uri::class);
         $uriMock->method('getQuery')
-                ->willReturn('Key=');
+            ->willReturn('Key=');
 
         $request = $this->createMock(Request::class);
         $request->method('getUri')
-                ->willReturn($uriMock);
+            ->willReturn($uriMock);
 
         $authenticator = new KeyAuthenticator('1234');
         $this->assertFalse($authenticator->isAuthorized($request));
     }
 
-    public function testIsAuthorizedWrongKey()
+    public function testIsAuthorizedWrongKey(): void
     {
         $uriMock = $this->createMock(Uri::class);
         $uriMock->method('getQuery')
-                ->willReturn('Key=foobar');
+            ->willReturn('Key=foobar');
 
         $request = $this->createMock(Request::class);
         $request->method('getUri')
-                ->willReturn($uriMock);
+            ->willReturn($uriMock);
 
         $authenticator = new KeyAuthenticator('1234');
         $this->assertFalse($authenticator->isAuthorized($request));
     }
 
-    public function testIsAuthorizedValidKey()
+    public function testIsAuthorizedValidKey(): void
     {
-        $shortenedTimestamp = substr(time(), 0, 7);
+        $shortenedTimestamp = substr((string)time(), 0, 7);
         $hash = hash_hmac('sha256', utf8_encode('1234'), utf8_encode($shortenedTimestamp));
         $encodedHash = base64_encode($hash);
         $calculatedKey = str_replace(['=', '/', '+'], '', $encodedHash);
 
         $uriMock = $this->createMock(Uri::class);
         $uriMock->method('getQuery')
-                ->willReturn('Key=' . $calculatedKey);
+            ->willReturn('Key=' . $calculatedKey);
 
         $request = $this->createMock(Request::class);
         $request->method('getUri')
-                ->willReturn($uriMock);
+            ->willReturn($uriMock);
 
         $authenticator = new KeyAuthenticator('1234');
         $this->assertTrue($authenticator->isAuthorized($request));
diff --git a/tests/autoload.php b/tests/autoload.php
index a745788..e2ef396 100644
--- a/tests/autoload.php
+++ b/tests/autoload.php
@@ -2,7 +2,7 @@
 /**
  * This file is part of the Billbee Custom Shop API package.
  *
- * Copyright 2019 by Billbee GmbH
+ * Copyright 2019-2022 by Billbee GmbH
  *
  * For the full copyright and license information, please read the LICENSE
  * file that was distributed with this source code.