ERR_NGROK_SHIP_ENVIRONMENT_VAR_KEY_NOT_ALLOWED: Environment variable KEY is reserved - ngrok documentation

What does ERR_NGROK_SHIP_ENVIRONMENT_VAR_KEY_NOT_ALLOWED mean?

ngrok returns ERR_NGROK_SHIP_ENVIRONMENT_VAR_KEY_NOT_ALLOWED with this message:

Environment variable <KEY> is reserved. ngrok sets 'PORT' and the 'PORT_' variables from the endpoint templates.

Where can I get more help with ERR_NGROK_SHIP_ENVIRONMENT_VAR_KEY_NOT_ALLOWED?

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