That error code usually means Nest Doorbell is trying to get its Wifi information from another Nest product in your home, and is unable to do so.
Temporarily remove other Nest products (except Google Wifi or Nest Wifi devices if you have them of course) from your home (i.e. other Nest Doorbell, Nest Protect, Nest thermostat, cameras etc) from the Nest app, then retry setup of your Nest Doorbell. Hopefully that works for you, and you can then re-add those other products back to the Nest app.
Alternatively, another workaround would be to create a new "home" in the app for your Nest Doorbell, as it then won't try to use another Nest product to get Wifi information. Of course that does mean your Nest Doorbell will be in its own "home" and there is no way to move products between homes.
