How to handle data messages for a terminated app

I am building a chat app where all the realtime messages will be delivered via FCM data messages and then conditionally show a notification using awesome_notifications. I had some problems at first like FCM background handler can’t update chats and chats’ messages if the app is in background, screen off, or even the user opened the status bar. I resolved those issues using an isolate with a receiver and send ports. everything is fine. The problem is if the app is completely terminated, nothing happens. I traced and checked all my code and everything. everything seems correct but when I try to run flutter run --release and see what it prints when the data message is sent. I get this:

E/flutter (23959): [ERROR:flutter/lib/ui/dart_runtime_hooks.cc(38)] Dart Error: Dart_LookupLibrary: library 'package:mobile_app_v2/services/firebase_helper.dart' not found.
E/flutter (23959): [ERROR:flutter/shell/common/shell.cc(117)] Dart Error: Dart_LookupLibrary: library 'package:mobile_app_v2/services/firebase_helper.dart' not found.
E/flutter (23959): [ERROR:flutter/shell/common/shell.cc(117)] Dart Error: Dart_LookupLibrary: library 'package:mobile_app_v2/services/firebase_helper.dart' not found.

all there is to know is that firebase_helper.dart is the file that has the initialization and binding of the FCM handlers like onMessage and onBackgroundMessage that is being called before runApp(const MyApp()); in main.dart.

firebase_helper.dart:

static void initializeFCMHandler() async {
FirebaseMessaging.onBackgroundMessage(handleBackgroundMessage);
FirebaseMessaging.onMessage.listen(handleMessage);
}

static Future<void> handleBackgroundMessage(RemoteMessage? message) async {
 NotificationService().pushNotification(
  id: 200,
  body: "Message From Background",
  title: "Conversations",
  category: NotificationCategory.Message,
  payload: {
    "screen": "chat",
  },
);
handleDataMessage(message, isBackground: true);
}

static void handleMessage(RemoteMessage? message) async {
// check if message is notification
print(message?.data);
if (message?.notification != null) {
  handleNotification(message);
} else {
  handleDataMessage(message);
}
}

I also tried building the app as apk and installing it but again no response. no notification, nothing. I searched and people actually can receive data messages successfully and everything works so where is the problem? I see people having a problem in iOS only.

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