ERR_NGROK_1952: The public key to sign in the certificate is required, but no public key was specified - ngrok documentation

What does ERR_NGROK_1952 mean?

ngrok returns ERR_NGROK_1952 with this message:

The public key to sign in the certificate is required, but no public key was specified.

Where can I get more help with ERR_NGROK_1952?

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