PayPal\PayPalAPI\DoExpressCheckoutPaymentReq::toXMLString PHP Method

    public function toXMLString()
    {
        $str = '';
        $str .= '<ns:DoExpressCheckoutPaymentReq>';
        if ($this->DoExpressCheckoutPaymentRequest != null) {
            $str .= '<ns:DoExpressCheckoutPaymentRequest>';
            $str .= $this->DoExpressCheckoutPaymentRequest->toXMLString();
            $str .= '</ns:DoExpressCheckoutPaymentRequest>';
        }
        $str .= '</ns:DoExpressCheckoutPaymentReq>';
        return $str;
    }