How to set Flutter FCM Background Notification Settings

Question

I don't have any problem with sending notifications. The only problem is that I can't set background notifications.

While notification importance and icon in onMessage method are working fine, but the icon is not visible in the background method and the notification priority is low.

How can I set icon and notification importance for background and terminated notifications.

Main

Future<void> backGroundHandler(RemoteMessage message) async {
  await Firebase.initializeApp();
}


const AndroidNotificationChannel channel = AndroidNotificationChannel(
  'high_importance_channel', // id
  'High Importance Notifications', // title
  description:
      'This channel is used for important notifications.', // description
  importance: Importance.high,
  playSound: false,
);

final FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin =
    FlutterLocalNotificationsPlugin();


void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  FirebaseMessaging.onBackgroundMessage(backGroundHandler);

  await FirebaseMessaging.instance.setForegroundNotificationPresentationOptions(
    alert: true,
    badge: true,
    sound: false,
  );
  
  await flutterLocalNotificationsPlugin
      .resolvePlatformSpecificImplementation<
          AndroidFlutterLocalNotificationsPlugin>()
      ?.createNotificationChannel(channel);

Notification page (onMessage)

class NotificationAlert extends GetxController {
  void getNotify() {
    FirebaseMessaging.onMessage.listen((RemoteMessage message) {
      RemoteNotification? notification = message.notification;
      AndroidNotification? android = message.notification?.android;
      if (notification != null && android != null) {
        flutterLocalNotificationsPlugin.show(
          notification.hashCode,
          notification.title,
          notification.body,
          NotificationDetails(
            android: AndroidNotificationDetails(
              channel.id,
              channel.name,
              channelDescription: channel.description,
              color: Color(0xFFAC0B35), //Colors.blue, //channel.ledColor,
              playSound: channel.playSound,
              icon: '@mipmap/ic_launcher',
            ),
          ),
        );
      }
    });
  }

  @override
  void onInit() {
    getNotify();
    super.onInit();
  }
}