ERR_NGROK_SHIP_REGISTRY_HOST_ILLEGAL_CHARACTER: The 'host' value HOST contains the illegal character CHAR - ngrok documentation

What does ERR_NGROK_SHIP_REGISTRY_HOST_ILLEGAL_CHARACTER mean?

ngrok returns ERR_NGROK_SHIP_REGISTRY_HOST_ILLEGAL_CHARACTER with this message:

The 'host' value <HOST> contains the illegal character <CHAR>. Use a hostname with an optional port, and no scheme or path.

Where can I get more help with ERR_NGROK_SHIP_REGISTRY_HOST_ILLEGAL_CHARACTER?

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