mastodon/docs/Using-the-API/Push-notifications.md

Push notifications

Mastodon can communicate with the Firebase Cloud Messaging API to send push notifications to apps on users' devices. For this to work, these conditions must be met:

• Responsibility of an instance owner: FCM_API_KEY set on the instance. This can be obtained on the Firebase dashboard, in project settings, under Cloud Messaging, as "server key"
• Responsibility of the app developer: Firebase added/enabled in the Android/iOS app. See Guide

When the app obtains/refreshes a registration ID from Firebase, it needs to send that ID to the /api/v1/devices/register endpoint of the authorized user's instance via a POST request. The app can opt out of notifications by sending a similiar request with unregister instead of register.

The push notifications will be triggered by the notifications of the type you can normally find in /api/v1/notifications. However, the push notifications will not contain any inline content. They will contain JSON data of this format ("12" is an example value):

{ notification_id: 12 }

Your app can then retrieve the actual content of the notification from the /api/v1/notifications/12 API endpoint.