C# Web Forms集成PayPal Smart Button时购物车总价传入OrderRequest失败

• 初始化顺序错位：你将OrderRequest定义成了类级别的字段初始化器，C#的类字段初始化逻辑早于Page_Load事件执行，这时候给price赋值的代码还没运行，price为空自然传不进值；加上PayPal SDK对金额字段的空值校验是静默忽略不抛错，所以你看不到任何报错提示。
• 金额格式不兼容：你用String.Format("{0:c}")生成的总价是带本地货币符号（如$、¥）的本地化字符串，PayPal接口的Money.Value字段只接受不带货币符号、固定两位小数、以英文点为小数点的纯数字字符串，带格式化符号的内容就算传进去也会被接口丢弃。

1. 调整金额生成逻辑
   保留页面展示用的带货币符号的格式，单独生成符合PayPal要求的纯数字金额：

   // 页面展示用的格式化文本，保持原有逻辑
   Lbl01.Text = String.Format("{0:c}", cartTotal);
   // PayPal接口用的金额文本，用固定格式生成避免本地化问题
   price = cartTotal.ToString("F2", System.Globalization.CultureInfo.InvariantCulture);
   

2. 调整OrderRequest的初始化时机
   不要在类定义时直接初始化OrderRequest对象，先声明空对象，等Page_Load中拿到有效总价之后，再手动构造订单请求实例，把对应金额字段替换成动态值：

   // 类内字段先声明，不直接初始化
   public OrderRequest orderRequest;
   
   protected void Page_Load(object sender, EventArgs e)
   {
       // 原有购物车总价计算逻辑保持不变
       using (ShoppingCartActions usersShoppingCart = new ShoppingCartActions())
       {
           decimal cartTotal = usersShoppingCart.GetTotal();
           Lbl01.Text = String.Format("{0:c}", cartTotal);
           price = cartTotal.ToString("F2", System.Globalization.CultureInfo.InvariantCulture);
       }
   
       // 拿到有效价格后再初始化订单请求
       orderRequest = new OrderRequest()
       {
           CheckoutPaymentIntent = "CAPTURE",
           // 原有ApplicationContext配置完全保留
           ApplicationContext = new ApplicationContext
           {
               BrandName = "EXAMPLE INC",
               LandingPage = "BILLING",
               CancelUrl = "https://www.example.com",
               ReturnUrl = "https://www.example.com",
               UserAction = "CONTINUE",
               ShippingPreference = "SET_PROVIDED_ADDRESS"
           },
           PurchaseUnits = new List<PurchaseUnitRequest>
           {
               new PurchaseUnitRequest{
                   ReferenceId =  "ReferenceId1",
                   Description = "Description1",
                   CustomId = "CustomId1",
                   SoftDescriptor = "SoftDescriptor1",
                   AmountWithBreakdown = new AmountWithBreakdown
                   {
                       CurrencyCode = Currency,
                       // 总金额必须和下方所有分项加总一致，否则会被校验拦截
                       Value = (cartTotal + 15 + 5 + 10 - 10).ToString("F2", System.Globalization.CultureInfo.InvariantCulture),
                       AmountBreakdown = new AmountBreakdown
                       {
                           ItemTotal = new Money
                           {
                               CurrencyCode = Currency,
                               Value = price // 此时可以正常取到计算好的购物车总价
                           },
                           // 原有运费、处理费、税费、折扣的配置保持不变
                           Shipping = new Money
                           {
                               CurrencyCode = Currency,
                               Value = "15.00"
                           },
                           Handling = new Money
                           {
                               CurrencyCode = Currency,
                               Value = "5.00"
                           },
                           TaxTotal = new Money
                           {
                               CurrencyCode = Currency,
                               Value = "10.00"
                           },
                           ShippingDiscount = new Money
                           {
                               CurrencyCode = Currency,
                               Value = "10.00"
                           }
                       }
                   },
                   // 原有Items、ShippingDetail配置保持不变，需要动态替换的商品单价也用同样的格式处理
                   Items = new List<Item>
                   {
                       new Item
                       {
                           Name = "Product 1",
                           Description = "Product 1 Description",
                           Sku = "Sku1",
                           UnitAmount = new Money
                           {
                               CurrencyCode = Currency,
                               Value = "100.00" // 如果要动态替换成购物车商品单价，同样用固定格式转字符串即可
                           },
                           Tax = new Money
                           {
                               CurrencyCode = Currency,
                               Value = "10.00"
                           },
                           Quantity = "1",
                           Category = "PHYSICAL_GOODS"
                       },
                   },
                   ShippingDetail = new ShippingDetail
                   {
                       Name = new Name
                       {
                           FullName = ""
                       },
                       AddressPortable = new AddressPortable
                       {
                           AddressLine1 = "",
                           AdminArea2 = "",
                           AdminArea1 = "",
                           PostalCode = "",
                           CountryCode = ""
                       }
                   }
               }
           }
       };
   }
   

3. 额外校验规则：PayPal接口要求AmountWithBreakdown的顶层总金额，必须严格等于所有分项金额的计算和（商品总金额+运费+处理费+税费-运费折扣），金额对不上也会被接口静默拦截不返回报错。

内容的提问来源于stack exchange，提问作者Arachai