ERR_NGROK_8004: Failed to establish tunnel protocol connection to HOST with error: ERR - ngrok documentation

What does ERR_NGROK_8004 mean?

ngrok returns ERR_NGROK_8004 with this message:

Failed to establish tunnel protocol connection to <HOST> with error: <ERR>

Troubleshoot ERR_NGROK_8004 with your AI agent. Connect it to the ngrok MCP server, then ask what caused the error and how to fix it.

Where can I get more help with ERR_NGROK_8004?

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