The WHMCS SDK can be installed with Composer. Run this command:
composer require perryfaro/sdk-whmcs
$authentication = new Whmcs\Authentication\Authentication;
$authentication->setUrl('https://www.example.com/');
$authentication->setPassword('password');
$authentication->setUsername('username');
Below you will see three ways of making a request.
Option 1:
$class = new Whmcs\Whmcs($authentication);
$class->client()->getClients()->request();
Option 2:
$class = new Whmcs\Client\Client($authentication);
$class->getClients()->request();
Option 3:
$class = new Whmcs\Client\Options\GetClients($authentication);
$class->request();