1st you need to have the rDNS configured to the FQDN of the server.
Then login to the server using the server name (e.g. server.domain.com)
https://server.doian.com:2031.
You will get that the site is not secure, and continue.
Under Server Settings -> Change Hostname
It will show:
Your Hostname is: server.domain.com and it resolves to IP: xxx.xxx.xxx.xxx
rDNS/PTR = server.domain.com
SUCCESSScroll down, and click on the Blue Bar that says, Change Hostname.
Give it a few seconds, depending on your servers speed.
This will create the SSL for the hostname, and secure the login screens.
Close the windows, and reopen, now when you login to
https://server.doman.com:2031 it will have a valid SSL.