我正在使用PayPal IPN来处理网站上的付款。我希望用户能够输入折扣代码和价值（金额或百分比），并将其传递给PayPal并计算。
我已经在网络上寻找，但似乎只找到以下内容：
Use discount_amount_cart to charge a single discount amount for the entire cart.
Use discount_amount_x to set a discount amount associated with item x
Use discount_rate_cart to charge a single discount percentage for the entire cart.
discount_rate_cart - Applies to entire cart however, this variable will only work with the "Upload" Method. Not the standard Add to Cart variables.
在我的请求字符串中测试了这些内容：
...&discount_amount_cart=10&...
PayPal似乎无法识别这个折扣。在PayPal IPN中还存在吗？
谢谢您的帮助！