stripeConfig.swift

func paymentAuthorizationViewController(_ controller: PKPaymentAuthorizationViewController, didAuthorizePayment payment: PKPayment, completion: @escaping (PKPaymentAuthorizationStatus) -> Void) {
    STPAPIClient.shared().createToken(with: payment) { (token: STPToken?, error: Error?) in
        guard let token = token, error == nil else {
            // Present error to user...
            return
        }

        submitTokenToBackend(token, completion: { (error: Error?) in
            if let error = error {
                // Present error to user...

                // Notify payment authorization view controller
                completion(.failure)
            }
            else {
                // Save payment success
                paymentSucceeded = true

                // Notify payment authorization view controller
                completion(.success)
            }
        })
    }
}