Some things to check:

My guess-->

Did you started xcode by double clicking the "runner.xcworkspace" from your "project/ios" folder and not "runner.xcodeproj"?

-Did you have it in pubspec.yaml if you have dependecy there?

dependencies:
   awesome_notifications: ^0.10.0

-Did you imported the package?

import 'package:awesome_notifications/awesome_notifications.dart';