ERR_NGROK_7042: Invalid edge module, OAuth cookie prefix PREFIX must consist of only alphanumeric characters with periods - ngrok documentation

What does ERR_NGROK_7042 mean?

ngrok returns ERR_NGROK_7042 with this message:

Invalid edge module, OAuth cookie prefix <PREFIX> must consist of only alphanumeric characters with periods.

Where can I get more help with ERR_NGROK_7042?

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