/**
  * SagePay throws an error if passed an IPv6 address.
  * Filter out addresses that are not IPv4 format.
  */
 public function getClientIp()
 {
     $ip = parent::getClientIp();
     // OmniPay core could do with a helper for this.
     if (!preg_match('/^[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}$/', $ip)) {
         $ip = null;
     }
     return $ip;
 }