ERR_NGROK_6528: Traffic made it to the ngrok edge, but there are no endpoints online serving an app - ngrok documentation

What does ERR_NGROK_6528 mean?

ngrok returns ERR_NGROK_6528 with this message:

Traffic made it to the ngrok edge, but there are no endpoints online serving an app.

Where can I get more help with ERR_NGROK_6528?

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