I'm trying to create a push service for my Android app, and I follow Google GCM's documentation and example for this matter:
I can register/unregister my Android app. From my server side, I can see that I have one subscription registered, but when I try to send a message from server to my Android app I always get following error:
Error sending message to device #0: MismatchSenderId
Did your server use the new registration ID returned by the GCM server to your app? I had this problem, if trying to send a message to registration IDs that are given out by the old C2DM server.
And also double check the Sender ID and API_KEY, they must match or else you will get that MismatchSenderId error. In the Google API Console, look at the URL of your project:
The xxxxxxxxx is the project ID, which is the sender ID.
And make sure the API Key belongs to 'Key for server apps (with IP locking)'