ERR_NGROK_4115: The email domain "DOMAIN" does not allow account creation - ngrok documentation

What does ERR_NGROK_4115 mean?

ngrok returns ERR_NGROK_4115 with this message:

The email domain "<DOMAIN>" does not allow account creation. Contact your ngrok administrator or support@ngrok.com for access.

Where can I get more help with ERR_NGROK_4115?

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