WHMCS can manage Plesk from inside itself. The following steps will walk you through adding a server to WHMCS that is using Plesk 11-12.
To create a server that is assigned to your Plesk go to Setup > Products/Services > Products/Services > Servers.
Inside this menu click on “Add New Server.”
On this page will you need to insert the following information regarding your server:
Name of server
Hostname of server
Server IP address
IP addresses assigned to the server
Monthly fees for server
The maximum number of accounts that can be placed on the server
Nameservers for the server along with each IP address for the Nameserver.
All of this information is inside your Plesk control panel. After your server information is added, select “Plesk” from the drop down list and enter your login username and password in the “Server Details” section.
Once selecting Plesk from the server list and you have added your login username and password click on the red “Test Connection” button to make sure the server is configured correctly.
After you have finished testing your server, mark the “Secure” box to use the SSL mode for all connections from WHMCS to your Plesk server. Once you have completed this last step, click on “Save Changes” to finish adding your Plesk server.