Cannot request a custom bind port '-R port:'.
You may either specify a reserved TCP address with '-R address:port:' or you may let the server choose a random remote port for you with '-R 0:'.
Example: ssh -R 0:localhost:22 ...
Example: ssh -R 1.tcp.eu.ngrok.io:21412:localhost:22 ...
If you're having trouble resolving this error, please reach out to support@ngrok.com.