PayPal Express DoExpressCheckoutPayment收费金额

这不是一个编码问题,但我想了解发生了什么。这是我第一次必须集成PayPal,所以我使用了一个沙盒环境和带有硬编码值的简单示例来开始。

对于SetExpressCheckoutRequest,假设支付值为x,一切正常(买家同意,令牌返回)。然后我意识到需要DoExpressCheckoutPayment来完成它,所以我使用了更多的示例代码,它也很好。

在DoExpressCheckoutPayment代码示例中,假定支付值为y。如前所述,我只是想让基本的工作原理发挥作用,而不想费心把价值观等联系起来。

现在让我惊讶的是:PayPal沙盒账户中显示的实际交易金额不是买家批准的x值,而是DoExpressCheckoutPayment的y值。这里是简化的示例代码:

    public ActionResult RunSample()
    {
        //...
        PaymentDetailsItemType[] pdItem = new PaymentDetailsItemType[1];
        pdItem[0] = new PaymentDetailsItemType()
        {
            Amount = new BasicAmountType() { currencyID = CurrencyCodeType.USD, Value = 1.50},
            //...
        };

        var resp = new PayPalAPIAAInterfaceClient().SetExpressCheckout(ref type, req);

        //...

        return new RedirectResult(string.Format("{0}?cmd=_express-checkout&token={1}",
            "https://www.sandbox.paypal.com/cgi-binwebscr?cmd=_express-checkout&token=EC-xxxxx", resp.Token));
    }

    public ActionResult RunSampleResult(string token, string payerId)
    {
        // result returned, buyer agreed to 1.50

        var NVP = "METHOD=DoExpressCheckoutPayment";

        //NVP += ...;
        NVP += "&PAYMENTREQUEST_0_AMT=100";

        HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://api-3t.sandbox.paypal.com/nvp");
        //...

        string sResponse = string.Empty;
        using (StreamWriter sw = new StreamWriter(request.GetRequestStream()))
        {
            sw.Write(NVP);
        }

        HttpWebResponse response = request.GetResponse() as HttpWebResponse;

        // => 100 is charged, not the 1.50 agreed to
    }

这只是沙盒行为吗?当然,要推翻买家同意的价值不那么容易吗?我错过了什么?