The [APNS 2 documentation](https://developer.apple.com/documentation/usernotifications/setting_up_a_remote_notification_server/handling_notification_responses_from_apns#3394529) includes a reason with the following details: Status Code: `400` Error String: `ExpiredToken` Description: `The device token has expired` All of the other reasons are [provided here](https://github.com/sideshow/apns2/blob/master/response.go#L16), but not this one.