src/Ovh/Cdn/Cdn.php
public function orderBackend($nbBackend, $duration)
    {
        return json_decode(self::getClient()->orderBackend($this->sn, $nbBackend, $duration));
    }
public function orderBackend($nbBackend, $duration)
    {
        return json_decode(self::getClient()->orderBackend($this->sn, $nbBackend, $duration));
    }
Order backend and return a billing order object

@param int $nbBackend : number of backend needed
@param int $duration : durtaion (in month)
@return object billing order