ERR_NGROK_9004: Your legacy account is not authorized to use response headers

What does ERR_NGROK_9004 mean?

ngrok returns ERR_NGROK_9004 with this message:

Your legacy account is not authorized to use response headers.

Upgrade to a new paid plan at: https://dashboard.ngrok.com/billing/choose-a-plan

Troubleshoot ERR_NGROK_9004 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.