override func viewDidLoad() {
    super.viewDidLoad()

    // Toggle apple pay button state
    applePayButton.enabled = Stripe.deviceSupportsApplePay()
}

- (void)viewDidLoad {
  [super viewDidLoad];

  // Toggle apple pay button state
  self.applePayButton.enabled = [Stripe deviceSupportsApplePay];
}

func handleApplePayButtonTapped() {
    let merchantIdentifier = "com.merchant.your_application"
    let paymentRequest = Stripe.paymentRequest(withMerchantIdentifier: merchantIdentifier, country: "US", currency: "USD")

    // Configure the line items on the payment request
    paymentRequest.paymentSummaryItems = [
        PKPaymentSummaryItem(label: "Fancy Hat", amount: 50.00),
        // The final line should represent your company;
        // it'll be prepended with the word "Pay" (i.e. "Pay iHats, Inc $50")
        PKPaymentSummaryItem(label: "iHats, Inc", amount: 50.00),
    ]

    // Continued in next step
}

- (void)handleApplePayButtonTapped {
    NSString *merchantIdentifier = @"com.merchant.your_application";
    PKPaymentRequest *paymentRequest = [Stripe paymentRequestWithMerchantIdentifier:merchantIdentifier country:@"US" currency:@"USD"];

    paymentRequest.paymentSummaryItems = @[
      [PKPaymentSummaryItem summaryItemWithLabel:@"Fancy Hat" amount:[NSDecimalNumber decimalNumberWithString:@"50.00"]],
      // The final line should represent your company;
      // it'll be prepended with the word "Pay" (i.e. "Pay iHats, Inc $50")
      [PKPaymentSummaryItem summaryItemWithLabel:@"iHats, Inc" amount:[NSDecimalNumber decimalNumberWithString:@"50.00"]],
    ];

    // Continued in next step
}

func handleApplePayButtonTapped() {
    let paymentRequest = ... // From previous step

    if Stripe.canSubmitPaymentRequest(paymentRequest) {
        // Setup payment authorization view controller
        let paymentAuthorizationViewController = PKPaymentAuthorizationViewController(paymentRequest: paymentRequest)
        paymentAuthorizationViewController.delegate = self

        // Present payment authorization view controller
        present(paymentAuthorizationViewController, animated: true)
    }
    else {
        // There is a problem with your Apple Pay configuration
    }
}

- (void)handleApplePayButtonTapped {
    PKPaymentRequest *paymentRequest = ...; // From previous step

    if ([Stripe canSubmitPaymentRequest:paymentRequest]) {
        // Setup payment authorization view controller
        PKPaymentAuthorizationViewController *paymentAuthorizationViewController = [[PKPaymentAuthorizationViewController alloc] initWithPaymentRequest:paymentRequest];
        paymentAuthorizationViewController.delegate = self;

        // Present payment authorization view controller
        [self presentViewController:paymentAuthorizationViewController animated:YES completion:nil];
    }
    else {
        // There is a problem with your Apple Pay configuration
    }
}

extension MyCheckoutViewController: STPAuthenticationContext {
func authenticationPresentingViewController() -> UIViewController {
    return self
}

func prepareAuthenticationContextForPresentation(completion: @escaping STPVoidBlock) {
    if presentedViewController != nil {
        dismiss(animated: true) {
            completion()
        }
    } else {
        completion()
    }
}
}

#pragma mark - STPAuthenticationContext

- (UIViewController *)authenticationPresentingViewController {
return self;
}

- (void)prepareAuthenticationContextForPresentation:(STPVoidBlock)completion {
if (self.presentedViewController != nil) {
    [self dismissViewControllerAnimated:YES completion:^{
        completion();
    }];
} else {
    completion();
}
}

func paymentAuthorizationViewController(_ controller: PKPaymentAuthorizationViewController, didAuthorizePayment payment: PKPayment, handler: @escaping (PKPaymentAuthorizationResult) -> Void) {
    let finishWithStatus: (PKPaymentAuthorizationStatus) -> Void = { status in
        if controller.presentingViewController != nil {
            // Notify PKPaymentAuthorizationViewController
            completion(PKPaymentAuthorizationResult(status: status, errors: nil))
        } else {
            // PKPaymentAuthorizationViewController was dismissed
            self.finish()
        }
    };

    STPAPIClient.shared().createPaymentMethod(with: payment) { (paymentMethod: STPPaymentMethod?, error: Error?) in
        guard let paymentMethod = paymentMethod, error == nil else {
            // Present error to customer...
            return
        }

        let clientSecret = ...// the client secret of the Payment Intent you created at the beginning of your checkout flow
        let paymentIntentParams = STPPaymentIntentParams(clientSecret: clientSecret)
        paymentIntentParams.paymentMethodParams = paymentMethodParams

        // Confirm the Payment Intent with the payment method
        STPPaymentHandler.shared().confirmPayment(paymentIntentParams, with: self) { (status, paymentIntent, error) in
            switch (status) {
                case .succeeded:
                    // Save payment success
                    self.paymentSucceeded = true
                    finishWithStatus(.success)
                case .canceled:
                    finishWithStatus(.failure)
                case .failed:
                    // Save error
                    self.paymentError = error
                    finishWithStatus(.failure)
            }
        }
    }
}

func paymentAuthorizationViewControllerDidFinish(_ controller: PKPaymentAuthorizationViewController) {
    // Dismiss payment authorization view controller
    dismiss(animated: true, completion: {
        self.finish()
    })
}

func finish() {
    if (paymentSucceeded) {
        // Show a receipt page...
    } else {
        // Present error to customer...
    }
}

- (void)paymentAuthorizationViewController:(PKPaymentAuthorizationViewController *)controller didAuthorizePayment:(PKPayment *)payment handler:(void (^)(PKPaymentAuthorizationResult *result))completion {
    void (^finishWithStatus)(PKPaymentAuthorizationResult) = ^(PKPaymentAuthorizationStatus status) {
        if (controller.presentingViewController != nil) {
            // Notify PKPaymentAuthorizationViewController
            completion([PKPaymentAuthorizationResult alloc] initWithStatus:status errors:nil]);
        } else {
            // PKPaymentAuthorizationViewController was dismissed
            [self _finish];
        }
    };

    [[STPAPIClient sharedClient] createPaymentMethodWithPayment:payment completion:^(STPPaymentMethod *paymentMethod, NSError *error) {
        if (paymentMethod == nil || error != nil) {
            // Present error to customer...
            return;
        }

        NSString *clientSecret = ...// the client secret of the Payment Intent you created at the beginning of your checkout flow
        STPPaymentIntentParams *paymentIntentParams = [[STPPaymentIntentParams alloc] initWithClientSecret:clientSecret];
        paymentIntentParams.paymentMethodParams = paymentMethodParams;

        // Confirm the Payment Intent with the payment method
        [[STPPaymentHandler sharedHandler] confirmPayment:paymentIntentParams
                                withAuthenticationContext:self
                                                completion:^(STPPaymentHandlerActionStatus status, STPPaymentIntent * paymentIntent, NSError * error) {
            switch (status) {
                case STPPaymentHandlerActionStatusSucceeded:
                    // Save payment success
                    self.paymentSucceeded = YES;

                    finishWithStatus(PKPaymentAuthorizationStatusSuccess);
                    break;
                case STPPaymentHandlerActionStatusCanceled:
                    finishWithStatus(PKPaymentAuthorizationStatusFailure);
                    break;
                case STPPaymentHandlerActionStatusFailed:
                    // Save error
                    self.paymentError = error;

                    finishWithStatus(PKPaymentAuthorizationStatusFailure);
                    break;
            }
        }];
    }
}

- (void)paymentAuthorizationViewControllerDidFinish:(PKPaymentAuthorizationViewController *)controller {
    [self dismissViewControllerAnimated:YES completion:^{
        [self _finish];
    }];
}

- (void)_finish {
    if (self.paymentSucceeded) {
        // Show a receipt page...
    } else {
        // Present error to customer...
    }
}