HTTPS monitoring on custom ports

Hello I'm trying to monitor HTTPS on custom port (18100).

I'm putting the port number in the port box. Also i've tried to with and without the port number in the url (https://blabla.blalbla.com:18100/bla/bla).

Unfortunately i'm getting 503 in solarwinds. In browser it works  , but in solarwinds not.

Any ideas ?

Thanks in advance

Ed