> ## Documentation Index
> Fetch the complete documentation index at: https://ngrok.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Error 3004

## ERR\_NGROK\_3004

ngrok gateway error: The server returned an invalid or incomplete HTTP response.

### Additional Information

This error usually occurs when users are hosting a secure upstream service (`https://localhost:[PORT]`) but have not configured the ngrok agent to send HTTPS traffic to it.

### Possible Solutions

* When starting the ngrok agent, use the full upstream service address. For example: `ngrok http https://localhost:8081`.

## Further help

If you're having trouble resolving this error, please reach out to [support@ngrok.com](mailto:support@ngrok.com?subject=Help%20with%20ERR_NGROK_3004)