We are using fcm to send push notifications. Recently we noticed some of our ios devices were not receiving push notifications, failing. By using the Push notification console we can see we are failing from APNS, with a 400 - Invalid Push Notification. Once this occurs we dont get push notifications on that device. We have tried re-logging in and re-installing the app. This does not work initially. However eventually they start working again after re-installing, usually after at least a day. { "code": 400, "message": "bad-request", "reason": "Invalid push token", "requestUuid": "ee04b0f1-c6aa-4b5e-87c0-7df754801d6f" } Any ideas why the token is deemed invalid? Is there any way to get more details?