ERR_NGROK_SHIP_PUBLISH_TARGET_HOST_UNSUPPORTED: A KIND publish target always publishes to FIXEDHOST - ngrok documentation

What does ERR_NGROK_SHIP_PUBLISH_TARGET_HOST_UNSUPPORTED mean?

ngrok returns ERR_NGROK_SHIP_PUBLISH_TARGET_HOST_UNSUPPORTED with this message:

A <KIND> publish target always publishes to <FIXEDHOST>. The 'host' value <HOST> is not allowed.

Where can I get more help with ERR_NGROK_SHIP_PUBLISH_TARGET_HOST_UNSUPPORTED?

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