Cause of the Issue It turned out that I had accidentally deleted a section of code inside lib/convert/json.dart, which happened to contain the jsonEncode definition. (Lesson learned: stop coding when you're tired! 😅) Steps to Fix It Check if convert.dart or related core files were modified If you find any missing code, restore it manually or reset your changes. Repair the Flutter pub cache flutter pub cache repair Delete the Flutter cache manually Navigate to your Flutter installation folder and delete the cache: flutter doctor Restart your IDE and rebuild the project