public function DoExpressCheckoutPayment($doExpressCheckoutPaymentReq, $apiCredential = null)
{
$apiContext = new PPApiContext($this->config);
$handlers = array(new PPMerchantServiceHandler($apiCredential, self::$SDK_NAME, self::$SDK_VERSION));
$this->setStandardParams($doExpressCheckoutPaymentReq->DoExpressCheckoutPaymentRequest);
$ret = new DoExpressCheckoutPaymentResponseType();
$resp = $this->call('PayPalAPIAA', 'DoExpressCheckoutPayment', $doExpressCheckoutPaymentReq, $apiContext, $handlers);
$ret->init(PPUtils::xmlToArray($resp));
return $ret;
}