Push token
The changeable address for one installed copy of your app, used by APNs or FCM to deliver a push notification to that device.
See it
What it is
A push token is the opaque address APNs or FCM gives one app install. Your app sends it to your backend, and the backend attaches it to a notification request so the push service knows which installed copy should receive the message. It is not a user ID and it is not the phone's permanent identity.
Register for one during notification setup and sync it to the backend with the signed-in account, platform, and app environment. A single person may have several valid tokens across a phone, tablet, work profile, or reinstall, so store a collection rather than one token column on the user.
Gotcha: tokens rotate. APNs can return a new device token when the app launches, and FCM calls its refresh callback when a registration token changes. Upsert the latest value, remove tokens when a provider reports them unregistered, and never use the token itself as proof that a request came from a particular user.
Ask AI for it
Implement push token registration for APNs and Firebase Cloud Messaging. On iOS, forward the token from application(_:didRegisterForRemoteNotificationsWithDeviceToken:); on Android, read FirebaseMessaging.getInstance().getToken() and handle FirebaseMessagingService.onNewToken(). Upsert each token to the backend with user ID, platform, app bundle or package ID, environment, locale, app version, and last-seen timestamp. Support several tokens per user, move a token safely when accounts change on one device, delete it on sign-out, and mark it inactive when APNs or FCM returns an unregistered response. Never treat a push token as authentication.