Braintree Paypal Checkout错误:SFSafariViewController不会切换回应用程序

Question

我正在使用Xcode 8,swift 3.通过carthage和braintree版本4.7.2安装.

点击继续沙盒购买按钮它没有回到应用程序并且没有收到响应并且没有收到错误.

在安装过程中我有什么遗漏

我正在按时结账使用PayPal.

              @IBAction func customPayPalButtonPressed(_ sender: AnyObject) {


                    let payPalDriver : BTPayPalDriver = BTPayPalDriver.init(apiClient: self.apiClient!)

                    payPalDriver.viewControllerPresentingDelegate = self
                    payPalDriver.appSwitchDelegate = self

                    let payPalRequest = BTPayPalRequest(amount: "100.00")
                    payPalRequest.currencyCode = "USD"
                    payPalDriver.requestOneTimePayment(payPalRequest) { (tokenizedPayPalAccount, error) -> Void in

                        if (tokenizedPayPalAccount != nil) {

                            print(tokenizedPayPalAccount.debugDescription)
                        }else if (error != nil) {
                            print(error?.localizedDescription)
                            print(error.debugDescription)
                        }else {

                            print("Cancled")

                        }
                    }



                }