52119: FCM could not deliver to iOS device: APNs token is unregistered

Twilio attempted to send a push notification to an iOS device through Firebase Cloud Messaging (FCM). FCM then forwarded the notification to Apple Push Notification service (APNs). APNs rejected the request because the device token is no longer registered, so the notification wasn't delivered.

Twilio deleted the Binding that contained this device token and won't attempt to send additional notifications to it.

This error is specific to iOS devices reached through an FCM Credential.

• The user uninstalled your app from the iOS device.
• The user disabled push notifications for your app, or the device token was invalidated by iOS (for example, after a restore onto a different device).
• The APNs device token was registered against a different environment (sandbox versus production) than the one your FCM project is configured to use, so APNs no longer recognizes it.
• Your application stored a device token that has since been replaced, and it registered the stale token with Twilio.

• Register a new Binding whenever your app receives an updated device token from iOS, so notifications continue to reach the user after they reinstall or re-enable notifications.
• Confirm that your app requests the device token on every launch and creates or updates the Binding with the value iOS returns, rather than caching a token indefinitely.
• Verify that the APNs environment your app builds against matches the APNs configuration uploaded to your Firebase project.

• The provided APNs device token has been unregistered — the same failure when Twilio delivers to APNs directly, using an APNs Credential.
• GCM/FCM client uninstalled or turned off notifications — the same failure for an Android device token.

• Notify Bindings resource
• Notify Credentials resource