(ISSUE) flutterEngine.getPlugins().add(new io.github.ponnamkarthik.toast.fluttertoast.FlutterToastPlugin())

The same issue occured in my case
So, i tried multiple things and somehow this worked for me

flutter clean
dart pub cache repair
flutter pub get
flutter build apk --build-name 1.2.3 --build-number 1

Add these 4 commands in your terminal one by one. May it works for you ☺️