If you are installing an SSL cert on a domain within Plesk you will first need to set the domain to use a dedicated or exclusive IP address. Please see here for how to add a second IP address to your Cloud VM plan:
With our legacy VPS packages you can add up to two separate IP addresses and if you haven't done so already you can add another IP address to your VPS in the main control panel under:
VPS > IP Addresses > Add new IP address
You might need to make sure the appropriate subscription is selected in the Subscription drop down menu first if you have multiple subscriptions
If this option is greyed out then it means you have to purchase an extra IP address as you already have two assigned to your VPS. Or you can use the second IP address you added to the VPS if you aren't using it already.
Once the second IP address is added you can then log in to the Plesk control panel and go to:
Server >> IP Addresses >> *the second IP address*
and change the IP address from Shared to Exclusive and click 'Ok'.
Once the second IP address is added you will have to unassign it from the My Domains client in Plesk itself under:
Clients > My Domains > IP Addresses > tick the box beside the second IP address and click Remove IP address (this is only possible if the IP address isn't assigned to a domain)
Now change the IP address to exclusive under Settings > IP Addresses > click on the icon to the left of the new IP address
Then add the IP address back to the client's IP Pool:
Clients > My Domains > IP Addresses > Add new IP address
Assign the IP address to the domain:
To assign the domain to this exclusive IP address and thus assign your SSL cert to it go to:
Domains >> *domainname* >> Setup or Web Hosting Settings (depending on Plesk version)
You can pick the second, dedicated IP address from the "IP Addresses" drop down menu and then a new drop down menu should appear for your "Certificate".
First you will have had to have purchased\set up a new IP address on your VM itself:
Once you have done that note down your new IP address and log in to your Plesk control panel. Then go to:
Tools & Utilities > IP Addresses > Reread IP
Plesk should then automatically pick up any new IP addresses you set up on the VM. It will most likely set it to dedicated by default so if you want to change that just click on the new IP address itself and change it to Shared if you want.
For how to generate the SSL cert you can look here:
Setting up an SSL cert in Plesk