ERR_NGROK_SHIP_CHATBOT_SUBSCRIPTION_SUBJECT_UNSUPPORTED: REF is not something I can subscribe to - ngrok documentation

What does ERR_NGROK_SHIP_CHATBOT_SUBSCRIPTION_SUBJECT_UNSUPPORTED mean?

ngrok returns ERR_NGROK_SHIP_CHATBOT_SUBSCRIPTION_SUBJECT_UNSUPPORTED with this message:

<REF> is not something I can subscribe to. Known namespaces: <NAMESPACES>.

Where can I get more help with ERR_NGROK_SHIP_CHATBOT_SUBSCRIPTION_SUBJECT_UNSUPPORTED?

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