iOS 上的 StoreKit - 自动更新订阅 - 如何知道它是否是免费试用

Swift
import StoreKit
func checkSubscriptionTrialStatus() {
    if let receiptURL = Bundle.mAIn.appStoreReceiptURL,
       let receiptData = try? Data(contentsOf: receiptURL),
       let receiptString = receiptData.base64EncodedString(options: []) {
        let requestDictionary = ["receipt-data": receiptString]
        do {
            let requestData = try JSONSerialization.data(withJSONObject: requestDictionary, options: [])
            let validationURLString = "Apple.com/verifyReceipt">https://sandbox.itunes.Apple.com/verifyReceipt</a>" // Use production URL for live app
            let validationURL = URL(string: validationURLString)!
            var request = URLRequest(url: validationURL)
            request.httpMethod = "POST"
            request.httpBody = requestData
            
            let session = URLSession.shared
            let task = session.dataTask(with: request) { (data, response, error) in
                if let data = data,
                   let JSonResponse = try? JSONSerialization.JSonObject(with: data, options: []) as? [String: Any],
                   let receiptInfo = JSonResponse["receipt"] as? [String: Any],
                   let inAppPurchases = receiptInfo["in_app"] as? [[String: Any]] {
                    for purchase in inAppPurchases {
                        if let isTrialPeriod = purchase["is_trial_period"] as? String {
                            // 订阅是免费试用
                            if isTrialPeriod == "true" {
                                print("订阅为免费试用")
                            } else {
                                print("订阅不是免费试用")
                            }
                        }
                    }
                }
            }
            task.resume()
        } catch {
            print("请求验证凭证失败")
        }
    }
}