I recommend switching to the ModulesGarden one recently released. https://www.modulesgarden.com/products/whmcs/vultr-vps
- WHMCS version 7.2.x or newer
- PHP version 7.1.x or newer
- MySQL 5.6, MariaDB 5.6, MariaDB 10.0, or MariaDB 10.1
- ionCube Loader
- Vultr API Key
- Your WHMCS Server IPs being whitelisted for API Access
See the WHMCS Module documentation.