public function Pay($payRequest, $apiCredential = NULL)
{
$ret = new PayResponse();
$apiContext = new PPApiContext($this->config);
$handlers = array(new PPPlatformServiceHandler($apiCredential, self::$SDK_NAME, self::$SDK_VERSION));
$resp = $this->call('AdaptivePayments', 'Pay', $payRequest, $apiContext, $handlers);
$ret->init(PPUtils::nvpToMap($resp));
return $ret;
}