I'm building an app in react native, and I attached react-native-fcm library to the code, in order to work with notification messages.
I have two main problems:
1) Notification from the firebase doesn't look like the ordinary notification messages: it's not appear with app icon, it doesn't popup and presented when the screen is closed.
2) I wanted just to get the event of messaging, also here after reviewing the library code, I saw that notification get to the function: onMessageReceived only if the app on foreground, like it say in the website.
But in the website I couldn't understand how to get the general event of catching notificaiton regardless to the appstate.
I also tried to implement class that extends FirebaseMessagingService, and there the notification doesn't get to the onMessageReceived override at all.
You will need to use FCM API and send data in data field instead of using Firebase console or notification field so that the method onMessageReceived is always called regardless of whether the app is in foreground or background. When this method is called, you can create a notification as you like.
Read about FCM admin API at: https://firebase.google.com/docs/cloud-messaging/admin/
Read about FCM HTTP API at: https://firebase.google.com/docs/cloud-messaging/http-server-ref
You can use Postman to send notification if you choose to use FCM HTTP API.