I changed it, but still I get the same error msg :(
Mátyás Kőne

I have some ideas to debug:
Add --verboseto the mos command to see more details of the error.
See if the registry is correctly created on Google Cloud Console.

You already flashed the firmware in the device ? 
Run mos ui and try to connect to the device, flash the iot-kit-* firmware and try to register again with GCP.

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