iOS应用内购(IAP)促销优惠报错：该优惠仅面向当前/过往订阅用户

问题背景 #

已在App Store Connect完成应用内购（IAP）促销优惠配置，通过后端生成签名（signature）、随机数（nonce）和时间戳（timestamp）后，初始化SKPaymentDiscount方法时触发如下错误：

This offer is available only to current or previous subscribers of this app.
[Environment: Xcode]

开发参考Apple官方文档实现，相关代码如下：

PrepareForOffer 代码 #

func prepareOffer(usernameHash: String, productIdentifier: String, offerIdentifier: String, completion: @escaping (SKPaymentDiscount) -> Void) {

    let applicationUserName = UUID().uuidString.lowercased()
    let param:[String:Any] = ["productIdentifier": productIdentifier,
                              "applicationUsername": applicationUserName,
                              "offerID": offerIdentifier]
    param.printJson()
    APIManager.sharedInstance.usersAPIManager.GetSignatureData(params: param, success: { (responseObject) in
        self.purchase = Mapper<IAPModel>().map(JSON: responseObject as [String: Any])
        
        // Create offer
        var uuid = UUID(uuidString: self.purchase?.nonce ?? "")
        let discountOffer = SKPaymentDiscount(identifier: offerIdentifier, keyIdentifier: "5WWL777LG5", nonce: uuid ?? UUID(), signature: self.purchase?.signature ?? "", timestamp: (self.purchase?.timestamp ?? 0) as NSNumber)

        // Pass offer in completion block
        completion(discountOffer)
    }) { (error) in
        print(error)
    }
}

BuyProduct 代码 #

func buyProduct(product: SKProduct, forApplicationUsername usernameHash: String, withOffer offer: SKPaymentDiscount) {

    print("buyProduct", offer.debugDescription.description)
  // Create payment object
  let payment = SKMutablePayment(product: product)

  // Apply username and offer to the payment
  payment.applicationUsername = usernameHash
  payment.paymentDiscount = offer

  // Add payment to paymentQueue
  InAppPurchaseManager.shared.paymentQueue.add(payment)
}

排查与解决步骤 #

1. 确认优惠的受众配置 #

先检查App Store Connect里的优惠类型：

• 如果配置的是挽留优惠或订阅升级/降级优惠，这类优惠仅对现有/曾订阅过的用户开放，测试时必须用有订阅记录的沙盒账号（可以先订阅基础套餐，再测试优惠）；
• 如果是给新用户的优惠，要选择“新订阅用户”类型（比如介绍优惠、新用户定向促销优惠）。

2. 修复applicationUsername不一致问题 #

代码里存在关键参数不匹配的问题：

• prepareOffer中生成了新的UUID作为applicationUsername传给后端生成签名；
• 但buyProduct里却用了外部传入的usernameHash赋值给payment.applicationUsername。

Apple要求生成签名时的applicationUsername必须和发起支付时的完全一致，否则会触发权限校验错误。修改方案：
把prepareOffer里的applicationUserName换成传入的usernameHash，保证前后参数统一，修改后的代码片段：

func prepareOffer(usernameHash: String, productIdentifier: String, offerIdentifier: String, completion: @escaping (SKPaymentDiscount) -> Void) {

    // 直接使用传入的usernameHash，避免前后参数不一致
    let applicationUserName = usernameHash
    let param:[String:Any] = ["productIdentifier": productIdentifier,
                              "applicationUsername": applicationUserName,
                              "offerID": offerIdentifier]
    param.printJson()
    APIManager.sharedInstance.usersAPIManager.GetSignatureData(params: param, success: { (responseObject) in
        self.purchase = Mapper<IAPModel>().map(JSON: responseObject as [String: Any])
        
        // 增加nonce有效性校验，不要直接用默认UUID
        guard let nonceStr = self.purchase?.nonce, let uuid = UUID(uuidString: nonceStr) else {
            print("后端返回的nonce无效")
            return
        }
        let discountOffer = SKPaymentDiscount(identifier: offerIdentifier, keyIdentifier: "5WWL777LG5", nonce: uuid, signature: self.purchase?.signature ?? "", timestamp: (self.purchase?.timestamp ?? 0) as NSNumber)

        completion(discountOffer)
    }) { (error) in
        print(error)
    }
}

3. 验证后端签名逻辑 #

• 确认后端生成签名时使用的applicationUsername、productIdentifier、offerIdentifier和客户端传入的完全一致；
• 检查后端用的签名密钥（Key ID和私钥）是否和App Store Connect中配置的优惠密钥匹配；
• 确保时间戳是秒级UNIX时间戳，且和客户端初始化SKPaymentDiscount的时间差不超过5分钟。

4. 检查沙盒账号状态 #

如果用沙盒账号测试：

• 若优惠面向老用户，确认账号之前订阅过该产品（即使已过期）；
• 可以在测试设备的「设置」->「Apple ID」->「媒体与购买项目」->「查看账户」->「订阅」里确认账号的订阅记录。

内容的提问来源于stack exchange，提问作者Imran