We have an app for iOS and Android that uses GCM. I\'m trying to upload a new production APNS certificate to GCM but I can\'t because Google is moving GCM to Firebase.
I would suggest that you move to Firebase Cloud Messaging (FCM). If you go to the Firebase console you will be able to create a new Firebase project or import an existing Google project. Once you are in your Firebase project you will be able to connect your iOS and Android apps. You can then upload your APNs cert there.
See the docs for more details on connecting iOS apps and uploading APNs cert to Firebase.