diff --git a/lib/apis/sign_api/i_sign_engine_app.dart b/lib/apis/sign_api/i_sign_engine_app.dart
index 182fe411..c393d4ea 100644
--- a/lib/apis/sign_api/i_sign_engine_app.dart
+++ b/lib/apis/sign_api/i_sign_engine_app.dart
@@ -27,7 +27,7 @@ abstract class ISignEngineApp extends ISignEngineCommon {
   void registerEventHandler({
     required String chainId,
     required String event,
-    required dynamic Function(String, dynamic)? handler,
+    dynamic Function(String, dynamic)? handler,
   });
   Future<void> ping({
     required String topic,