ERR_NGROK_1940: Key size is supported only with a key type of "rsa", but the specified key type was "KEYTYPE" - ngrok documentation

What does ERR_NGROK_1940 mean?

ngrok returns ERR_NGROK_1940 with this message:

Key size is supported only with a key type of "rsa", but the specified key type was "<KEYTYPE>".

Where can I get more help with ERR_NGROK_1940?

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