In order to use the SSL feature your site must have it's own static (dedicated) IP address. If you don't have a dedicated IP address, you will get an error message when you access the SSL menu:
Could not execute your request
Details: You are not allowed to modify your SSL
Contact your web host for information on obtaining a dedicated IP address. Please note that some web hosts don't offer dedicated IP's, and hosts that do usually charge extra for this feature.
Why do I need an owned IP address?
Triple DES certificates don't work through DirectAdmin.