Service wont initialize when exported to seperate class

Question

Whenever I am trying to launch background service from a seperate class then it doesn't work at all, nothing happens. However when I include all the methods under void main() in main.dart file and in main use await initializeService(); then it works. Why I can't launch this from an external class that I have created? I don't want to keep all the methods in the main file because it's getting messy. Am I doing something wrong? I am using this library https://pub.dev/packages/flutter_background_service

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await BackgroundService().initializeService();
  child: const MyApp()));
}

class BackgroundService {

  Future<void> initializeService() async {
    final service = FlutterBackgroundService();
    await service.configure(
      androidConfiguration: AndroidConfiguration(
        // this will executed when app is in foreground or background in separated isolate
        onStart: onStart,

        // auto start service
        autoStart: true,
        isForegroundMode: true,
      ),
      iosConfiguration: IosConfiguration(
        // auto start service
        autoStart: true,

        // this will executed when app is in foreground in separated isolate
        onForeground: onStart,

        // you have to enable background fetch capability on xcode project
        onBackground: onIosBackground,
      ),
    );
  }

// to ensure this executed
// run app from xcode, then from xcode menu, select Simulate Background Fetch
  void onIosBackground() {
    WidgetsFlutterBinding.ensureInitialized();
    print('FLUTTER BACKGROUND FETCH');
  }

  void onStart() {
    WidgetsFlutterBinding.ensureInitialized();
    final service = FlutterBackgroundService();
    service.onDataReceived.listen((event) {
      if (event!["action"] == "setAsForeground") {
        service.setForegroundMode(true);
        return;
      }

      if (event["action"] == "setAsBackground") {
        service.setForegroundMode(false);
      }

      if (event["action"] == "stopService") {
        service.stopBackgroundService();
      }
    });

    // bring to foreground
    service.setForegroundMode(true);
    Timer.periodic(const Duration(seconds: 3), (timer) async {
      if (!(await service.isServiceRunning())) timer.cancel();
      service.setNotificationInfo(
        title: "My App Service",
        content: "Updated at ${DateTime.now()}",
      );

      print("Hello");
      service.sendData(
        {
          "current_date": DateTime.now().toIso8601String(),
          // "device": device,
        },
      );
    });
  }
}