Accept a payment with Link

First, you need a Stripe account. Register now.

Server-side

This integration requires endpoints on your server that communicate with the Stripe API. Use the Stripe official libraries for access to the Stripe API from your server.

# For detailed setup, see our quickstarts at https://stripe.com/docs/development/quickstart
bundle add stripe
bundle install

Client-side

The Stripe iOS SDK is open source, fully documented, and compatible with apps supporting iOS 13 or above.

When your app starts, configure the SDK with your Stripe publishable key so that it can make requests to the Stripe API.

import UIKit
import StripePaymentSheet

@UIApplicationMain
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
    }
}

curl https://api.stripe.com/v1/payment_intents \
  -u 
sk_test_4eC39HqLyjWDarjtT1zdp7dc
: \
  -d "amount"=1099 \
  -d "currency"="usd" \
  -d "payment_method_types[]"="link" \
  -d "payment_method_types[]"="card"

Instead of passing the entire PaymentIntent object to your app, only return its client secret. The PaymentIntent’s client secret is a unique key that lets you confirm the payment and update card details on the client, without allowing manipulation of sensitive information, like payment amount.

Before displaying the mobile Payment Element, your checkout page should:

• Show the products being purchased and the total amount
• Collect any required shipping information
• Include a checkout button to present Stripe’s UI

Next, integrate Stripe’s prebuilt payment UI into your app’s checkout with the PaymentSheet class.

import UIKit
import StripePaymentSheet

class CheckoutViewController: UIViewController {
  @IBOutlet weak var buyButton: UIButton!
  var paymentSheet: PaymentSheet?
  let backendCheckoutUrl = URL(string: "Your backend endpoint")! // Your backend endpoint

  override func viewDidLoad() {
    super.viewDidLoad()

    buyButton.addTarget(self, action: #selector(didTapCheckoutButton), for: .touchUpInside)
    buyButton.isEnabled = false

    // MARK: Fetch the PaymentIntent and Customer information from the backend
    var request = URLRequest(url: backendCheckoutUrl)
    request.httpMethod = "POST"
    let task = URLSession.shared.dataTask(with: request, completionHandler: { [weak self] (data, response, error) in
      guard let data = data,
            let json = try? JSONSerialization.jsonObject(with: data, options: []) as? [String : Any],
            let paymentIntentClientSecret = json["paymentIntent"] as? String,
            let self = self else {
        // Handle error
        return
      }

      // MARK: Create a PaymentSheet instance
      var configuration = PaymentSheet.Configuration()
      configuration.merchantDisplayName = "Example, Inc."

      self.paymentSheet = PaymentSheet(paymentIntentClientSecret: paymentIntentClientSecret, configuration: configuration)

      DispatchQueue.main.async {
        self.buyButton.isEnabled = true
      }
    })
    task.resume()
  }

}

@objc
func didTapCheckoutButton() {
  // MARK: Start the checkout process
  paymentSheet?.present(from: self) { paymentResult in
    // MARK: Handle the payment result
    switch paymentResult {
    case .completed:
      print("Your order is confirmed")
    case .canceled:
      print("Canceled!")
    case .failed(let error):
      print("Payment failed: \n\(error.localizedDescription)")
    }
  }
}

If PaymentSheetResult is .completed, inform the user (for example, by displaying an order confirmation screen).

PaymentSheet stores some cookies locally to remember the customer across sessions. For example, they’re used when a customer signs into their Link account. These cookies must be deleted if the customer signs out of your app. When that happens, call the PaymentSheet.resetCustomer() method, and the Stripe SDK will clear the internal state of PaymentSheet.

import UIKit
import StripePaymentSheet

class MyViewController: UIViewController {

  @objc
  func didTapLogoutButton() {
    PaymentSheet.resetCustomer()
    // Other logout logic required by your app
  }

}

Currently Link only works with credit and debit cards. To give your customers more payment options at checkout, Stripe is working to add additional funding sources (like bank accounts) to Link in 2022. Periodically test your checkout flow to confirm the look and feel of your payments screen is what you expect.

You can create test mode accounts for Link using any valid email address. The following table shows the fixed one-time passcode values that Stripe accepts for authenticating test mode accounts:

For testing specific payment methods, refer to the Payment Element testing examples.

Multiple funding sources

Link only works with cards currently, but it can automatically support additional funding sources, such as banks, as we add them. This means your customers can save and reuse their preferred payment method to check out faster on your app without any programmatic changes to your integration. When we add new funding source options to Link, we still instantly confirm the payment for your business and settle the transaction with the same timeline as cards.

To test that your integration can handle additional funding sources, provide an email in the form of {any_prefix}+multiple_funding_sources@{any_domain} when you create a test mode Link account. This flow will allow you to test Link with additional funding sources that are not currently available but may be coming to Link in the future.

Card authentication and 3D Secure

Link supports 3D Secure (3DS) authentication for card payments. 3DS requires customers to complete an additional verification step with the card issuer when paying. Payments that have been successfully authenticated using 3D Secure are covered by a liability shift.

To trigger 3DS authentication challenge flows with Link in test mode, use the following test card with any CVC, postal code, and future expiration date: 4000000000003220

In test mode, the authentication process displays a mock authentication page. On that page, you can either authorize or cancel the payment. Authorizing the payment simulates successful authentication and redirects you to the specified return URL. Clicking the Failure button simulates an unsuccessful attempt at authentication.

For more details, refer to the 3D Secure authentication page.