Accept a payment with Alma

import UIKit
import StripePaymentsUI

@main
class AppDelegate: UIResponder, UIApplicationDelegate {

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        StripeAPI.defaultPublishableKey = 
"pk_test_TYooMQauvdEDq54NiTphI7jx"
        // do any other necessary launch configuration
        return true
    }
}

class CheckoutViewController: UIViewController {
    var paymentIntentClientSecret: String?

    // ...continued from previous step

    override func viewDidLoad() {
        // ...continued from previous step
        startCheckout()
    }

    func startCheckout() {
        // Request a PaymentIntent from your server and store its client secret
        // Click View full sample to see a complete implementation
    }
}

// This method handles opening custom URL schemes (for example, "your-app://stripe-redirect")
func application(_ app: UIApplication, open url: URL, options: [UIApplication.OpenURLOptionsKey: Any] = [:]) -> Bool {
    let stripeHandled = StripeAPI.handleURLCallback(with: url)
    if (stripeHandled) {
        return true
    } else {
        // This was not a Stripe url – handle the URL normally as you would
    }
    return false
}

// This method handles opening universal link URLs (for example, "https://example.com/stripe_ios_callback")
func application(_ application: UIApplication, continue userActivity: NSUserActivity, restorationHandler: @escaping ([UIUserActivityRestoring]?) -> Void) -> Bool {
    if userActivity.activityType == NSUserActivityTypeBrowsingWeb {
        if let url = userActivity.webpageURL {
            let stripeHandled = StripeAPI.handleURLCallback(with: url)
            if (stripeHandled) {
                return true
            } else {
                // This was not a Stripe url – handle the URL normally as you would
            }
        }
    }
    return false
}

let paymentIntentParams = STPPaymentIntentParams(clientSecret: paymentIntentClientSecret)

// Alma does not require additional parameters so we only need to pass the initialized
// STPPaymentMethodAlmaParams instance to STPPaymentMethodParams
let alma = STPPaymentMethodAlmaParams()
let paymentMethodParams = STPPaymentMethodParams(alma: alma, billingDetails: nil, metadata: nil)

paymentIntentParams.paymentMethodParams = paymentMethodParams
paymentIntentParams.returnURL = "payments-example://stripe-redirect"

STPPaymentHandler.shared().confirmPayment(paymentIntentParams,
                                          with: self)
{ (handlerStatus, paymentIntent, error) in
    switch handlerStatus {
    case .succeeded:
        // Payment succeeded
        // ...

    case .canceled:
        // Payment canceled
        // ...

    case .failed:
        // Payment failed
        // ...

    @unknown default:
        fatalError()
    }
}