ERR_NGROK_412: Only accounts on paid plans can reserve endpoints on custom domains

What does ERR_NGROK_412 mean?

ngrok returns ERR_NGROK_412 with this message:

Only accounts on paid plans can reserve endpoints on custom domains.
Your account cannot reserve endpoints on custom domains (<DOMAIN> is not a subdomain of <BASE>).

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

Troubleshoot ERR_NGROK_412 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_412?

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