diff --git a/in_app_purchases/step_09/dart-backend/bin/server.dart b/in_app_purchases/step_09/dart-backend/bin/server.dart
index 48c77ed273..520e6f8ac5 100644
--- a/in_app_purchases/step_09/dart-backend/bin/server.dart
+++ b/in_app_purchases/step_09/dart-backend/bin/server.dart
@@ -92,7 +92,7 @@ Future<void> main() async {
   });
 
   // Start service
-  await serveHandler(router);
+  await serveHandler(router.call);
 }
 
 ({
diff --git a/in_app_purchases/step_09/dart-backend/pubspec.yaml b/in_app_purchases/step_09/dart-backend/pubspec.yaml
index 4d543b98a6..70d359a8fd 100644
--- a/in_app_purchases/step_09/dart-backend/pubspec.yaml
+++ b/in_app_purchases/step_09/dart-backend/pubspec.yaml
@@ -15,5 +15,5 @@ dependencies:
   app_store_server_sdk: ^1.2.5
 
 dev_dependencies:
-  lints: ^2.0.0
+  lints: ">=2.0.0 <4.0.0"
   test: ^1.16.0