In order to activate cPanel/WHM license on your server please perform these steps:
1. Buy license by providing existing VPS IP address: https://billing.time4vps.com/cart/licenses/
2. Install cPanel/WHM OS template from the VPS management panel
If you have installed cPanel/WHM OS template before license purchase, please login to VPS via SSH and execute:
/usr/local/cpanel/cpkeyclt
This will refresh license information.