Onesignal-flutter-sdk: Error Heads-up notification is not displayed in Android

[Santi92]

Description:*

Error Heads-up notification is not displayed in Android:
When I update version 3.0.0 oneSignal on Android the Heads-up notification is not displayed, but on IOS it is working fine.

Environment

flutter doctor
bash [✓] Flutter (Channel stable, 2.2.2, on macOS 11.2.3 20D91 darwin-x64, locale en-CO) [✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3) [✓] Xcode - develop for iOS and macOS [✓] Chrome - develop for the web [✓] Android Studio (version 4.2) [✓] IntelliJ IDEA Community Edition (version 2021.1.2) [✓] VS Code (version 1.57.1) [✓] Connected device (2 available)

pubspec
```yaml
name: xxxxxx
description: xxxxx

environment:
sdk: 2.13.3
flutter: 2.2.2

dependencies:
flutter:
sdk: flutter

onesignal_flutter: ^3.0.0

```

Steps to Reproduce Issue:

1. Create a notification at https://app.onesignal.com/apps/xxx/notifications/newt
2. Send notification

3. When it arrives only sounds and is not displaying Heads-up notification when the user is using the smart phone.

   Setup OneSignal:

    Future<void> init() async {
   await OneSignal.shared.setLogLevel(OSLogLevel.error, OSLogLevel.none);
   await OneSignal.shared.setRequiresUserPrivacyConsent(false);
   
    _initListeners();
   
    await OneSignal.shared.setAppId(_oneSignalAppId);
   }
   
   
   void _initListeners() {
   OneSignal.shared.setNotificationWillShowInForegroundHandler((event) {
     event.complete(event.notification);
   
     final payload = event.notification;
   
     final properties = _mapPropertiesForAnalytics(payload);
   
   
     handleReceive(payload.additionalData);
   });
   }
   

   SEARCH EXISTING ISSUES FOR relating to the same topic but not describing : https://github.com/OneSignal/OneSignal-Flutter-SDK/issues/421

   Please help me :white_frowning_face:

[jennantilla]

Have you set up categories for Android?

With Android 8+ you must add these custom features through notification Categories aka Channels. You can set these in the Settings > Messaging tab.

You will want to set the Importance to Urgent to accomplish this.

More information on Android Categories here: https://documentation.onesignal.com/docs/android-notification-categories

[Santi92]

Yes, thank you very much. 🥇
If, as I was sending it from one signal, I did not have it configured.

fixed.