I have been using Google Cloud Messaging to send messages to my phone via php pages on my permanently on server (a Raspberry Pi) successfully for some time. In that old app I used a browser key with no restrictions and not a server key.
I was aware that GCM should be migrated to Firebase Cloud Messaging (FCM) and have successfully done this. During development both FCM and GCM apps were working. Recently my GCM app returns Unauthorized (401) errors to my server. I know that FCM will only give out restricted server keys now and that unrestricted keys are not issued.
I am surprised that my old app developed before FCM even existed has stopped working. I assume that the message sent from my server to Google is being rejected by them.
Am I correct in my assumption that old GCM browser keys will always be rejected by Google?