[Register("AppDelegate")]
    public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate
    {
        public override bool FinishedLaunching(UIApplication app, NSDictionary options)
        {
            global::Xamarin.Forms.Forms.Init();
            LoadApplication(new App("",""));
            RequestPushPermissionsAsync();
            _launchoptions = options;
            return base.FinishedLaunching(app, options);
        }
        NSDictionary _launchoptions;
        public override void OnActivated(UIApplication uiApplication)
        {
            base.OnActivated(uiApplication);
            if (_launchoptions != null && _launchoptions.ContainsKey(UIApplication.LaunchOptionsRemoteNotificationKey))
            {
                var notfication = _launchoptions[UIApplication.LaunchOptionsRemoteNotificationKey] as NSDictionary;
                PresentNotification(notfication);
            }
            _launchoptions = null;
        }

        async Task RequestPushPermissionsAsync()
        {
            var requestResult = await UNUserNotificationCenter.Current.RequestAuthorizationAsync(
                 UNAuthorizationOptions.Alert
                | UNAuthorizationOptions.Badge
                | UNAuthorizationOptions.Sound);

            bool approved = requestResult.Item1;
            NSError error = requestResult.Item2;
            if (error == null)
            {
                if (!approved)
                {
                    Console.Write("Permission to receive notification was not granted");
                    return;
                }

                var currentSettings = await UNUserNotificationCenter.Current.GetNotificationSettingsAsync();
                if (currentSettings.AuthorizationStatus != UNAuthorizationStatus.Authorized)
                {
                    Console.WriteLine("Permissions were requested in the past but have been revoked (-Settings  app)");
                    return;
                }
                UIApplication.SharedApplication.RegisterForRemoteNotifications();
            }
            else
            {
                Console.Write($"Error requesting permissions: {error}.");
            }
        }

        public async override void RegisteredForRemoteNotifications(UIApplication application, NSData deviceToken)
        {
            if (deviceToken == null)
            {
                return;
            }
            Console.WriteLine($"Token received: {deviceToken}");
            await SendRegistrationTokenToMainPRoject(deviceToken);
        }

        async Task SendRegistrationTokenToMainPRoject(NSData deviceToken)
        {
            MessagingCenter.Send<object, string>(this, "fcmtoken", deviceToken.ToString());
        }

        public override void FailedToRegisterForRemoteNotifications(UIApplication application, NSError error)
        {
            Console.WriteLine($"Failed to register for remote notifications: {error.Description}");
        }

        public override void DidReceiveRemoteNotification(UIApplication application, NSDictionary userInfo,
            Action<UIBackgroundFetchResult> completionHandler)
        {
            PresentNotification(userInfo);
            completionHandler(UIBackgroundFetchResult.NoData);
            try
            {
                UIApplication.SharedApplication.ApplicationIconBadgeNumber = 0;
                NSDictionary aps = userInfo.ObjectForKey(new NSString("aps")) as NSDictionary;
                var message = (aps[new NSString("webContentList")] as NSString).ToString();
                LoadApplication(new App("", message));
            }
            catch (Exception ex)
            {
                //LogInfo.ReportErrorInfo(ex.Message, ex.StackTrace, "AppDelegate-DidReceiveRemoteNotification");
            }
        }

        void PresentNotification(NSDictionary userInfo)
        {
            NSDictionary aps = userInfo.ObjectForKey(new NSString("aps")) as NSDictionary;

            var msg = string.Empty;

            if (aps.ContainsKey(new NSString("alert")))
            {
                msg = (aps[new NSString("alert")] as NSString).ToString();
            }
            if (string.IsNullOrEmpty(msg))
            {
                msg = "(unable to parse)";
            }
            MessagingCenter.Send<object, string>(this, App.NotificationReceivedKey, msg);
        }
    }

{
    "multicast_id": 8754155136812875313,
    "success": 0,
    "failure": 1,
    "canonical_ids": 0,
    "results": [
        {
            "error": "InvalidRegistration"
        }
    ]
}

{
    "to" : "d20ad003 7473bfba 85dffc33 1534decf b4b886f1 c738878f fd7f2c60 d9dabc36",
 "collapse_key" : "type_a",
 "data" : {
     "body" : "Body of Your Notification in Data",
     "title": "Title of Your Notification in Title",
     "key_1" : "Value for key_1",
     "key_2" : "Value for key_2"
 },
 "notification" : {
     "body" : "Body of Your Notification",
     "title": "Title of Your Notification",
     "sound": "default",
     "content_available" : true
 }
}