使用SwiftyStoreKit兑换iOS应用的促销代码

Question

我正在使用SwiftyStoreKit处理我的应用程序中的订阅。但是，唯一无效的是兑换促销代码。我认为还原功能可以正常工作，但不能正常工作。看起来像这样：

@IBAction func restorePurchases(_ sender: Any) {
        guard isConnectedToNetwork() else { return }
        guard GlobalConstants.isSubscribed else {
            showAlertNothingToRestore()
            return
        }

        SwiftyStoreKit.restorePurchases(atomically: false) { results in
            if results.restoreFailedPurchases.count > 0 {
                log("Restore Failed: \(results.restoreFailedPurchases)")
            } else if results.restoredPurchases.count > 0 {
                for purchase in results.restoredPurchases where purchase.needsFinishTransaction {
                    // fetch content from your server, then:
                    SwiftyStoreKit.finishTransaction(purchase.transaction)
                }
                log("Restore Success: \(results.restoredPurchases)")
                let when = DispatchTime.now() + .seconds(1)
                DispatchQueue.main.asyncAfter(deadline: when) {
                    self.becomeMember()
                }
            } else {
                showAlertNothingToRestore()
            }
        }
    }

这只会导致“无法恢复”消息，并且促销代码无效。如何更改此代码以使其正常工作？