苹果支付PassKit里面presentationWindow函数如何写

请问苹果支付PassKit里面 PKPaymentAuthorizationControllerDelegate协议里面函数presentationWindow要怎么写？我这样写为什么不行？谢谢

func presentationWindow(for controller: PKPaymentAuthorizationController) -> UIWindow? {
let paymentWindow:UIWindow=UIWindow(frame: CGRect(x: 0,y: 0,width: 200,height: 200))
return paymentWindow
}

以下是startPayment函数

 func startPayment(completion: @escaping PaymentCompletionHandler) {
    
    let amount = PKPaymentSummaryItem(label: "Ammount", amount: NSDecimalNumber(string: price), type: .final)
    let tax = PKPaymentSummaryItem(label: "Tax", amount: NSDecimalNumber(string: "1.12"), type: .final)
    let total = PKPaymentSummaryItem(label: "ToTal", amount: NSDecimalNumber(string: "10.00"), type: .pending)

    paymentSummaryItems = [amount, tax, total];
    completionHandler = completion

    // Create our payment request
    let paymentRequest = PKPaymentRequest()
    paymentRequest.paymentSummaryItems = paymentSummaryItems
    paymentRequest.merchantIdentifier = "merchant.com.YOURDOMAIN.YOURAPPNAME"
    paymentRequest.merchantCapabilities = .capability3DS
    paymentRequest.countryCode = "US"
    paymentRequest.currencyCode = "USD"
    paymentRequest.requiredShippingContactFields = [.phoneNumber, .emailAddress]
    paymentRequest.supportedNetworks = PaymentHandler.supportedNetworks

    // Display our payment request
    paymentController = PKPaymentAuthorizationController(paymentRequest: paymentRequest)
    paymentController?.delegate = self
        //self.presentationWindow(for: paymentController!)
    paymentController?.present(completion: { (presented: Bool) in
        if presented {
            NSLog("Presented payment controller")
        } else {
            NSLog("Failed to present payment controller")
            self.completionHandler!(false)
         }
     })
    
  }