在 Rest API 中为销售退款PayPal 使用 C# 捕获了内部服务错误 500

我正在尝试退还PayPal的销售。我正在使用PayPal REST API。

这是我的示例代码：

APIContext apiContext = APiConfig();
Sale sale = Sale.Get(apiContext, "0D952456WY462504J");
Amount refundAmount = new Amount();
refundAmount.total = "0.01";
refundAmount.currency = currency;
Refund refund = new Refund();
refund.amount = refundAmount;
var newRefund = sale.Refund(apiContext, refund);
response = new PaypalResponse() {
       amount = newRefund.amount,
       create_time = Convert.ToDateTime(newRefund.create_time),
       update_time = Convert.ToDateTime(newRefund.update_time),
       state = newRefund.state,
       parent_payment = newRefund.parent_payment,
       id = newRefund.id
       };

在此行上收到错误："var new退款 = 销售。Refund（apiContext， Refund）;"它说：远程服务器返回错误：（500） 内部服务器错误。

谁能回答这个问题？谢谢！