ERR_NGROK_27203: Cannot use ngrok-managed key for unknown model "MODELID": pricing required for billing - ngrok documentation

What does ERR_NGROK_27203 mean?

ngrok returns ERR_NGROK_27203 with this message:

Cannot use ngrok-managed key for unknown model "<MODELID>": pricing required for billing.

Where can I get more help with ERR_NGROK_27203?

Email support@ngrok.com and include the error code.