Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpstan/phpstan-phpunit ^1.4.0 -> satisfiable by phpstan/phpstan-phpunit[1.4.0]. - phpstan/phpstan-phpunit 1.4.0 requires phpstan/phpstan ^1.11 -> found phpstan/phpstan[1.11.0, ..., 1.12.10] but it conflicts with your root composer.json require (^2.0.1). Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.