public class MainActivity : Xamarin.Forms.Platform.Android.FormsAppCompatActivity
{
public static readonly int NOTIFICATION_ID = 1000; <-- Important that it is 1000 in current plugin
public static readonly string CHANNEL_ID = "YourChannel";
internal static readonly string COUNT_KEY = "count";

        protected override void OnCreate(Bundle savedInstanceState)
        {
            TabLayoutResource = Resource.Layout.Tabbar;
            ToolbarResource = Resource.Layout.Toolbar;
            base.OnCreate(savedInstanceState);
            CreateNotificationChannel(); <--- important to call the setup function!

....
void CreateNotificationChannel()
  {
      if (Build.VERSION.SdkInt < BuildVersionCodes.O)
      {
          // Notification channels are new in API 26 (and not a part of the
          // support library). There is no need to create a notification
          // channel on older versions of Android.
          return;
      }

      var name = Resources.GetString(Resource.String.channel_name);
      var description = GetString(Resource.String.channel_description);
      var channel = new NotificationChannel(CHANNEL_ID, name, NotificationImportance.Max)
      {
          Description = description,
          LockscreenVisibility = NotificationVisibility.Public,
          Importance = NotificationImportance.Max,

      };

      var notificationManager = (NotificationManager)GetSystemService(NotificationService);
      notificationManager.CreateNotificationChannel(channel);
  }
}

public class NotificationsConfiguration : UNUserNotificationCenterDelegate
{
    public NotificationsConfiguration()
    {
    }

    #region Override Methods
    public override void WillPresentNotification(UNUserNotificationCenter center, UNNotification notification, Action<UNNotificationPresentationOptions> completionHandler)
    {
        // Do something with the notification
        Console.WriteLine("Active Notification: {0}", notification);

        // Tell system to display the notification anyway or use
        // `None` to say we have handled the display locally.
        completionHandler(UNNotificationPresentationOptions.Sound | UNNotificationPresentationOptions.Alert | UNNotificationPresentationOptions.Badge);
    }
    #endregion
}

  if (UIDevice.CurrentDevice.CheckSystemVersion(10, 0))
  {
      // Ask the user for permission to get notifications on iOS 10.0+
      UNUserNotificationCenter.Current.RequestAuthorization(
              UNAuthorizationOptions.Alert | UNAuthorizationOptions.Badge | UNAuthorizationOptions.Sound | UNAuthorizationOptions.CriticalAlert,
              (approved, error) => { Console.WriteLine(approved); });
  }
  else if (UIDevice.CurrentDevice.CheckSystemVersion(8, 0))
  {
      // Ask the user for permission to get notifications on iOS 8.0+
      var settings = UIUserNotificationSettings.GetSettingsForTypes(
              UIUserNotificationType.Alert | UIUserNotificationType.Badge | UIUserNotificationType.Sound,
              new NSSet());

      UIApplication.SharedApplication.RegisterUserNotificationSettings(settings);
  }

  UNUserNotificationCenter.Current.Delegate = new NotificationsConfiguration();

NotificationService.ShowNotification(title: "NotificationTitle",
                                     subtitle: "Quick Notification",
                                      body: "Alarming information",
                                      id: {currentlyUnusedSoJustPut1},
                                      notificationTime: TimeSpan.FromMinutes(30));

NotificationService.ShowNotification(title: "NotificationTitle",
                                     subtitle: "Quick Notification",
                                      body: "Alarming information",
                                      id: {currentlyUnusedSoJustPut1},
                                      notificationTime: new DateTimeOffset({someTimeHere));

NotificationService.CancelNotification({justleaveas1})