ERR_NGROK_SHIP_DOCKERFILE_READ_REFUSED: GitHub refused to read Dockerfile PATH from branch BRANCH (HTTP STATUS) - ngrok documentation

What does ERR_NGROK_SHIP_DOCKERFILE_READ_REFUSED mean?

ngrok returns ERR_NGROK_SHIP_DOCKERFILE_READ_REFUSED with this message:

GitHub refused to read Dockerfile <PATH> from branch <BRANCH> (HTTP <STATUS>). Check the ngrok GitHub app's access to the repository.

Where can I get more help with ERR_NGROK_SHIP_DOCKERFILE_READ_REFUSED?

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