ERR_NGROK_6525: A Failover Backend may not reference the backend ID because it is a BACKENDTYPE backend - ngrok documentation

What does ERR_NGROK_6525 mean?

ngrok returns ERR_NGROK_6525 with this message:

A Failover Backend may not reference the backend <ID> because it is a <BACKENDTYPE> backend.

Where can I get more help with ERR_NGROK_6525?

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