title: FCM giving internal server error after updating APNs push certificate
body: <p>We are using firebase (fcm) to send notifications to iOS users. The app is live on app store and has active users. Push notifications were working but stopped suddenly when we changed our APNs certificate and uploaded the same in FCM. After this certificate all the push notifications have stopped to iOS devices and fcm is just returning a "internal server error" error message. 
  We are in a very bad situation right now and would appreciate any help on this matter. Thanks in advance.</p>