Domain: Domain for which WHMCS single login settings are to be done is to be selected from the drop down.
Billing URL: WHMCS URL is added as the billing URL.
Admin username: The admin username for WHMCS is to be specified here.
Admin password: The admin password for WHMCS is to be specified here.
API key: The API key for WHMCS is to be mentioned here.
Status: The status can be either enabled or disabled from here.