ERR_NGROK_SHIP_ENDPOINT_URL_PRIVATE_HOSTNAME_NAME_REQUIRED: The FIELD hostname HOST has no name in front of its private suffix - ngrok documentation

What does ERR_NGROK_SHIP_ENDPOINT_URL_PRIVATE_HOSTNAME_NAME_REQUIRED mean?

ngrok returns ERR_NGROK_SHIP_ENDPOINT_URL_PRIVATE_HOSTNAME_NAME_REQUIRED with this message:

The <FIELD> hostname <HOST> has no name in front of its private suffix.

Where can I get more help with ERR_NGROK_SHIP_ENDPOINT_URL_PRIVATE_HOSTNAME_NAME_REQUIRED?

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