ERR_NGROK_3900: CEL interpolation was unsuccessful in action ACTIONTYPE field FIELD

What does ERR_NGROK_3900 mean?

ngrok returns ERR_NGROK_3900 with this message:

CEL interpolation was unsuccessful in action <ACTIONTYPE> field <FIELD>

Troubleshoot ERR_NGROK_3900 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.