I am building my custom app with my own Airnotifier server. Moodle Mobile integration branch 3.7.1, and the latest version of Airnotifier.
I managed to build Android app, and it can registers its token on Airnotifier server, but in the Device column, it shows Android not Android-fcm.
I can send a test notification with Airnotifier broadcast menu.
But it cannot receive notifications initiated from Moodle site. I changed the platform in mdl_user_devices table in database from "Android-fcm" to "Android", and now it can receive Moodle site notifications.
Although I have created a project in Android FCM Console, and downloaded the google-services.json file, it seems that it can receive notifications through GCM, not FCM.
On the FCM console, there is no sign of activity.