I am having problem with onselect notifcation webengage via FCM notification while onbackground state(onpaused) for my flutter application

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Dart

Flutter

I am receiving notification on all state(foreground, background(on-Paused), terminated(on-Detached)) but it's redirecting me to the intended url only in(foreground and terminated state). Surprisingly, on receiving notification during foreground state, on-select notification works on-Background state(on-Paused) as well and I am redirected to my intended url. But the main problem is while recieving notification on-background state(on-Paused) without receiving notification on foreground at first, it just redirects me to where I was.

What I have tried:

Here is the code I am currently working on:
void afterInitFirebase() async {
  NotificationSettings settings = await _firebaseMessaging.requestPermission(
    alert: true,
    announcement: false,
    badge: true,
    carPlay: false,
    criticalAlert: false,
    provisional: false,
    sound: true,
  );

  await _firebaseMessaging
      .subscribeToTopic(topic)
      .onError((error, stackTrace) => {print(error)});

  await _firebaseMessaging.getToken().then((value) => {
        Preference.setString(fcm_token, value),
      });

  await _firebaseMessaging.setForegroundNotificationPresentationOptions(
    alert: true,
    badge: true,
    sound: true,
  );

  await _firebaseMessaging.getInitialMessage().then((RemoteMessage? message) {    
    if (message != null) {
      // _handleIncomingLinks();
      MyNotification().initMessaging(message, isPush: true);
    }
  });

  FirebaseMessaging.onMessage.listen((RemoteMessage message) {
    displayNotification(message);
  });

  FirebaseMessaging.onBackgroundMessage(_firebaseMessagingBackgroundHandler);

  FirebaseMessaging.onMessageOpenedApp.listen((RemoteMessage message) {
    print("${message.from} =--> ON MESSAGE OPENED APP");
  });
}



void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  HttpOverrides.global = MyHttpOverrides();
  try {
    await Firebase.initializeApp().then((value) {
      afterInitFirebase();
    });
  } catch (e) {
    print(
      "EXCEPTION ON MAIN:" + e.toString(),
    );
  }

  final NotificationAppLaunchDetails? notificationAppLaunchDetails =
      await fitNotification.getNotificationAppLaunchDetails();
  final uri = await getInitialUri();
  String initialRoute = splash_page;
  String id = "0";
  if (notificationAppLaunchDetails!.didNotificationLaunchApp) {
    selectedNotificationPayload = notificationAppLaunchDetails.payload;

    print("payload $selectedNotificationPayload");

    var parts = selectedNotificationPayload?.split(SEPARATOR);

    if (parts != null) {
      if (parts[0] == "course" ||
          parts[0].toLowerCase() == "coursedetails" ||
          parts[0].toLowerCase() == "coursedetails") {
        id = parts[1];
        //course details page
        initialRoute = course_details;
      } else if (parts[0].toLowerCase() == "allcourse") {
        initialRoute = all_course;
        if (parts.length > 1) {
          id = parts[1];
        }
        print("payload: $initialRoute $id");
      } else if (parts[0].toLowerCase() == "allplan") {
        if (parts.length > 1) {
          id = parts[1];
        }
        initialRoute = "/allPlans";
      } else if (parts[0].toLowerCase() == "web") {
        id = parts[1];
        initialRoute = web_page;
      } else if (parts[0].toLowerCase() == "plan") {
        id = parts[1];
        initialRoute = plans_details_page;
      } else if (parts[0].toLowerCase() == "quiz") {
        initialRoute = web_page_entrance;
      } else if (parts[0].toLowerCase() == "wishlist") {
        initialRoute = route_wish_list;
      } else if (parts[0].toLowerCase() == "carts") {
        initialRoute = my_carts;
      } else {
        initialRoute = notification_page;
      }
    }
  }
  if (uri == null) {
  } else {
    String path = uri.toString();
    if (path.toLowerCase().contains("coursedetails") ||
        path.toLowerCase().contains("/home/course")) {
      String idStr = uri.path.substring(uri.path.lastIndexOf('/') + 1);
      id = idStr;
      initialRoute = course_details;
    }
  }

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

void displayNotification(RemoteMessage message) {
  log(message.data.toString());
  MyNotification().initMessaging(message);
}

Here is MyNotification class:

<pre lang="Dart"><pre>const String SEPARATOR = "|";

class MyNotification {
  void initMessaging(RemoteMessage message, {isPush: true}) async {
    var androidInit = AndroidInitializationSettings('ic_notification');
    var iosInit = IOSInitializationSettings();
    var initSetting =
        InitializationSettings(android: androidInit, iOS: iosInit);
    await fitNotification.initialize(initSetting,
        onSelectNotification: onSelectNotification);

    var rand = new Random();
    int id = 1;
    String? title = "";
    String? body = "";
    String? icon = "";
    String? type = "";
    String? itemId = "";
    String link = "";  
    if (message.notification != null) {
      title = "${message.notification?.title}";
      body = "${message.notification?.body}";
      icon = "${message.notification?.android?.imageUrl}";

      if (Platform.isAndroid) {
        icon = "${message.notification?.android?.imageUrl}";
      } else {
        icon = "${message.notification?.apple?.imageUrl}";
      }
    }   
    if (message.data['source'] == "webengage") {
      isPush = true;
      Map<String, dynamic> messageData =
          jsonDecode(message.data['message_data']);    
      if (messageData.containsKey("title")) {
        title = messageData["title"];
        body = messageData["message"];
      }

      if (messageData.containsKey("expandableDetails")) {    
        Map<String, dynamic> expDetail = messageData["expandableDetails"];
        if (expDetail.containsKey("image")) {
          icon = expDetail["image"];
        }
        if (expDetail.containsKey("style")) {
          if (expDetail['style'] == "RATING_V1" ||
              expDetail['style'] == "CAROUSEL_V1") {
            isPush = false;
          }
        }
      }

      if (messageData.containsKey("custom")) {
        List<dynamic> customData = messageData['custom'];
        print("element1: ${customData.toString()}");

        customData.forEach((element) {
          Map<String, dynamic> maps = element;

          var key = maps['key'];
          var value = maps['value'];    
          if (key == "itemId") {
            itemId = value;
          }

          if (key == "type") {
            type = value;
          }
        });
      }
    } else {
      if (message.data.containsKey("icon")) {
        icon = message.data['icon'];
      }

      if (message.data.containsKey("title")) {
        title = message.data['title'];
        body = message.data['body'];
      }

      if (message.data.containsKey("type")) {
        type = message.data['type'];
      }

      if (message.data.containsKey("itemId")) {
        itemId = message.data["itemId"];
      }
    }

    if (title?.isNotEmpty == true && body?.isNotEmpty == true) {
      showNotification(rand.nextInt(1000), title, body, icon,
          "${type}$SEPARATOR${itemId}$SEPARATOR${icon}",
          isPush: isPush);
    }
  }

  Future<Uint8List> _getByteArrayFromUrl(String url) async {
    final http.Response response = await http.get(Uri.parse(url));
    return response.bodyBytes;
  }

  Future<void> showNotification(int notificationId, String? notificationTitle,
      String? notificationContent, String? icon, String payload,
      {String channelId = '1234',
      String channelTitle = 'Android Channel',
      String channelDescription = 'Default Android Channel for notifications',
      Priority notificationPriority = Priority.high,
      Importance notificationImportance = Importance.max,
      bool isPush = true}) async {
    //with icon
    if (icon != null && icon.isNotEmpty) {
      final String bigPicturePath =
          await _downloadAndSaveFile(icon, 'bigPicture.jpg');

      final BigPictureStyleInformation bigPictureStyleInformation =
          BigPictureStyleInformation(
        FilePathAndroidBitmap(bigPicturePath),
        largeIcon: FilePathAndroidBitmap(bigPicturePath),
      );

      var androidPlatformChannelSpecifics = new AndroidNotificationDetails(
        channelId, channelTitle,
        channelDescription: channelDescription,
        playSound: false,
        importance: notificationImportance,
        priority: notificationPriority,
        styleInformation: bigPictureStyleInformation,
        icon: 'for_icon',
      );

      final IOSNotificationDetails iOSPlatformChannelSpecifics =
          IOSNotificationDetails(attachments: <IOSNotificationAttachment>[
        IOSNotificationAttachment(bigPicturePath)
      ]);
      final MacOSNotificationDetails macOSPlatformChannelSpecifics =
          MacOSNotificationDetails(attachments: <MacOSNotificationAttachment>[
        MacOSNotificationAttachment(bigPicturePath)
      ]);

      final NotificationDetails notificationDetails = NotificationDetails(
          iOS: iOSPlatformChannelSpecifics,
          macOS: macOSPlatformChannelSpecifics,
          android: androidPlatformChannelSpecifics);

      if (isPush) {
        await fitNotification.show(
          notificationId,
          notificationTitle,
          notificationContent,
          notificationDetails,
          payload: payload,
        );
      }
    } else {
      //with out icon
      var androidPlatformChannelSpecifics = new AndroidNotificationDetails(
        channelId,
        channelTitle,
        channelDescription: channelDescription,
        playSound: false,
        importance: notificationImportance,
        priority: notificationPriority,
        icon: 'for_icon',
      );

      final NotificationDetails platformChannelSpecifics =
          NotificationDetails(android: androidPlatformChannelSpecifics);

      if (isPush) {
        await fitNotification.show(notificationId, notificationTitle,
            notificationContent, platformChannelSpecifics,
            payload: payload);
      }
    }

    var parts = payload.split(SEPARATOR);
    var now = new DateTime.now();
    var formatter = new DateFormat('yyyy-MM-dd HH:mm:ss');
    String formattedDate = formatter.format(now);

    NotificationModelData model = NotificationModelData(
        courseId: parts[1],
        icon: "$icon",
        title: notificationTitle.toString(),
        description: notificationContent.toString(),
        type: parts[0],
        notifyTime: formattedDate,
        isRead: false,
        id: now.millisecondsSinceEpoch.toString());
    var db = AppDatabase.instance;
    db.into(db.notificationModel).insert(model).then(
          (value) => print(value),
        );
  }

  Future<String> _downloadAndSaveFile(String url, String fileName) async {
    final Directory directory = await getApplicationDocumentsDirectory();
    final String filePath = '${directory.path}/$fileName';
    final http.Response response = await http.get(Uri.parse(url));
    final File file = File(filePath);
    await file.writeAsBytes(response.bodyBytes);
    return filePath;
  }

  Future<dynamic> onSelectNotification(String? payload) async {
    selectedNotificationPayload = payload;    
    var parts = payload!.split(SEPARATOR);

    if (parts[0].toLowerCase() == "course") {
      //course details page
      Navigator.pushNamed(
          navigatorKey.currentState!.overlay!.context, course_details,
          arguments: <String, String>{
            'course_id': parts[1],
            'thumbnail': parts[2]
          });
    } else if (parts[0].toLowerCase() == "web") {
      await Navigator.pushNamed(
          navigatorKey.currentState!.overlay!.context, web_page,
          arguments: <String, String>{'paymentUrl': "${parts[1]}"});
    } else if (parts[0].toLowerCase() == "allcourse") {
      Navigator.pushNamed(
          navigatorKey.currentState!.overlay!.context, all_course,
          arguments: <String, String>{'course_id': "${parts[1]}"});
    } else if (parts[0].toLowerCase() == "plan") {
      Navigator.pushNamed(
          navigatorKey.currentState!.overlay!.context, plans_details_page,
          arguments: <String, String>{'plan_id': "${parts[1]}"});
    } else if (parts[0].toLowerCase() == "allplan") {
      Navigator.pushNamed(
          navigatorKey.currentState!.overlay!.context, all_plans,
          arguments: <String, String>{'id': "${parts[1]}"});
    } else if (parts[0].toLowerCase() == "quiz") {
      Navigator.of(navigatorKey.currentState!.overlay!.context)
          .pushNamed(web_page_entrance);
    } else {
      //notification page
      await Navigator.pushNamed(
          navigatorKey.currentState!.overlay!.context, notification_page);
    }
  }

This is my WebPage class:

var url = "";

class WebPage extends StatefulWidget {
  void launchURL() async {
    if (await canLaunch(url))
      await launch(url);
    else
      throw "Could not launch $url";
  }

  @override
  _WebPageState createState() => _WebPageState();
}

class _WebPageState extends State<WebPage>{

  bool isLoading = true;
  final _key = UniqueKey();
  Map? _arguments;     

 var _webViewController;



@override
  void initState() {
    super.initState();
    WidgetsBinding.instance!.addPostFrameCallback((timeStamp) {
        return widget.launchURL();
      });
  }
  @override
  Widget build(BuildContext context) {
    _arguments = ModalRoute.of(context)!.settings.arguments as Map?;

    if (_arguments?.containsKey("paymentUrl") == true) {
      url = _arguments!["paymentUrl"];
    } else if (_arguments?.containsKey("course_id") == true) {
      url = _arguments!["course_id"];
    } else {
      print(url);
    }
    return Scaffold(
      body: SplashPage(),
    );
  }
}