ERR_NGROK_3009: Received an HTTP network error (status code 0) from a backend

What does ERR_NGROK_3009 mean?

ngrok returns ERR_NGROK_3009 with this message:

ngrok gateway error: Received an HTTP network error (status code 0) from a backend

Troubleshoot ERR_NGROK_3009 with your AI agent. Connect it to the ngrok MCP server, then ask what caused the error and how to fix it.

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