PHP Lumen中的FAC（第一大西洋贸易）付款网关中的退款交易

Question

我已使用FAC（第一大西洋贸易公司）付款网关进行付款交易。最初，我创建了一个订单，并使用FAC网关支付了货款。已成功完成。现在，我正在为同一订单进行退款交易。但这是行不通的。我遵循与文档相同的步骤。请在下面找到我的代码。预先感谢

$xmlstr = <<<XML
<?xml version="1.0" encoding="UTF-8"?>
<TransactionModificationRequest xmlns="http://schemas.firstatlanticcommerce.com/gateway/data">
</TransactionModificationRequest>
XML;
$sxe = new \SimpleXMLElement($xmlstr);
$transactionDetails = $sxe->addChild('TransactionDetails');
$transactionDetails->addChild('AcquirerId', '464748');
$transactionDetails->addChild('Amount', '000000005500'); // $ 55
$transactionDetails->addChild('CurrencyExponent', 2);
$transactionDetails->addChild('MerchantId', 'xxxxx');
$transactionDetails->addChild('ModificationType', 2);
$transactionDetails->addChild('OrderNumber', 'ORD0035'); //Previously ordered number
$transactionDetails->addChild('Password', 'xxxxxx');
$xml = $sxe->asXML();
$ch = \curl_init("https://ecm.firstatlanticcommerce.com/PGServiceXML/TransactionModification");
curl_setopt($ch,CURLOPT_SSL_VERIFYHOST, 0);
curl_setopt($ch,CURLOPT_SSL_VERIFYPEER, 0);
curl_setopt($ch,CURLOPT_POST, 1);
curl_setopt($ch,CURLOPT_HTTPHEADER, array('Content-Type: text/xml'));
curl_setopt($ch,CURLOPT_POSTFIELDS, $xml);
curl_setopt($ch,CURLOPT_RETURNTRANSFER, 1);
$response = curl_exec($ch);
curl_close($ch);
print_r($response);

始终将响应返回为空。缺少代码上的任何内容？