ERR_NGROK_SHIP_DOCKERFILE_FROM_REQUIRED: Dockerfile PATH on branch BRANCH has no FROM instruction - ngrok documentation

What does ERR_NGROK_SHIP_DOCKERFILE_FROM_REQUIRED mean?

ngrok returns ERR_NGROK_SHIP_DOCKERFILE_FROM_REQUIRED with this message:

Dockerfile <PATH> on branch <BRANCH> has no FROM instruction.

Where can I get more help with ERR_NGROK_SHIP_DOCKERFILE_FROM_REQUIRED?

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