I uninstalled the Ring and Rapid Ring applications, re-installed, and attempted to use the Ring app to re-enable the indoor stick-up camera on my cellular network. It still gives the same error.
Interestingly, I can turn on motion alerts in the Rapid Ring application (see screenshot), but the settings don’t carry over in the Ring application. If I close the Rapid Ring application, the settings are saved, so I’m assuming that it’s been enabled but I’m not sure what zones are set.