Swift Checkout Implementation

The Swift Checkout SDK enables you to offer a complete and fast checkout experience to your end users from any point of your allows you to collect payment, address, and contact information with the click of a button.

Prerequisites

  • Add a payment method to your browser or wallet. For example, you can save a card in Chrome, add a card to your Apple Wallet for Safari and iOS

  • Serve your application over HTTPS. This is a requirement both in development and in production environments. One way to get up and running is to use a service like ngrok

Currently available payment methods through Swift Checkout SDK:

SumUp Swift Checkout SDK setup

Include the SDK.js in your page as shown below:

<script src="https://js.sumup.com/swift-checkout/v1/sdk.js"></script>

<div id="payment-request-button">
  <!-- Placeholder for the buttons. -->
</div>

Or with JavaScript:

function injectScript() {
  return new Promise((resolve) => {
    var script = document.createElement('script');
    script.type = 'text/javascript';
    script.onload = function () {
      resolve(window.SumUp);
    };
    script.src = 'https://js.sumup.com/swift-checkout/v1/sdk.js';
    document.body.appendChild(script);
  });
}

Once the script is loaded, a new SumUp object is injected into the window instance representing SumUp SDK namespace, which contains the SwiftCheckout client.

Obtaining a public API key

To obtain a public API key navigate to your Developer Settings Portal and select API keys from the top right corner menu. Your public merchant key will be automatically generated with a Private label and a value such as sup_pk_0x98lsJhJAs...u5kvg.

SumUp Swift Checkout client

const swiftCheckoutClient = window.SumUp.SwiftCheckout('sup_pk_0x98lsJhJAs...u5kvg');

The client contains a set of objects to render a payment element UI, request payment authorization and process a payment using SumUp’s API.

Payment request object

The payment request object requests payment authorizations made with various payment methods. It requires an argument that contains a set of details, information about the requested transaction to be processed, that will be presented to the user to authorize the payment later.

Payment request object arguments consist of:

  • countryCode: Represents the country or region of the merchant’s principle place of business.
  • total: Represents what is about to be paid by the user, E.g. a summary of an order. It requires a label and an amount.
const paymentRequest = swiftCheckoutClient.paymentRequest({
  countryCode: 'DE',
  total: {
    label: 'My goods',
    amount: { currency: 'EUR', value: '65.00' },
  },
});
  • shippingOptions: Represents a collection of shipping methods the end user can select from to receive their purchased goods. The initial shippingOptions list can be later modified according to the shipping address the user selects in the payment dialog.
const paymentRequest = swiftCheckoutClient.paymentRequest({
  shippingOptions: [
    {
      id: 'post',
      label: 'postal service',
      amount: { currency: 'EUR', value: '0.00' },
      description: 'free post',
    },
  ],
});

This object is an analogue to the PaymentRequest - Web APIs.

The payment request instance contains the logic related to checking payment method availability and showing the payment method dialogue once the user interacts with a payment element.

Payment request interface

All methods in the payment request object are asynchronous. Listed below are the payment request methods and their usage:

canMakePayment

Checks if the given merchant public key has access to at least one payment method and checks the payment method availability in the given environment (browser). Returns a promise that resolves in a boolean.

availablePaymentMethods

Returns the available payment methods for a merchant. Returns a promise that resolves in an array of objects representing each available payment method.

show

Shows the payment authorization dialogue for a given payment method. It requires an object containing a paymentMethod, which defines the selected payment method. This method is usually used along with the PaymentElement's onSubmit event.

The show method resolves with a AuthorizedPayment, which contains the details shared by the user once they authorize the payment request. The property details contains paymentMethod, contactInformation, shippingAddress and may contain shippingOptions.

A PaymentRequestCancelledError will be thrown when the user rejects or cancels the transaction.

paymentRequest
  .show({ paymentMethod: 'apple_pay' })
  .then(processCheckoutAttempt)
  .then(handleResponse)
  .catch((error) => {
    if (
      error instanceof SumUp.SwiftCheckout.Errors.PaymentRequestCancelledError
    ) {
      console.log('Cancelled by the user');
    } else {
      throw error;
    }
  });

abort

Terminates a payment request before it is processed. Once a payment request has been terminated using this method, the payment request will not be processed and the payment dialogue will be closed.

if (someCustomCheck()) {
  try {
    await paymentRequest.abort(); // will throw an error.
    console.log('Payment request aborted due to my custom reason.')
  } catch(e) {
    console.error(
    'Unable to abort, because the user is currently in the process of paying.'
    );
  }
}

onShippingAddressChange

Allows adding an event handler which will be triggered every time the user changes their shipping address. The handler can optionally provide a return value to change the following in the payment dialog:

  • total
  • shippingOptions
paymentRequest.onShippingAddressChange(async (newShippingAddress) => {
  const { total, shippingOptions } = await someAsyncOperation(
    newShippingAddress,
  );

  return {
    total,
    shippingOptions,
  };
});

onShippingOptionsChange

Allows adding an event handler which will be triggered every time the user changes their shipping option choice. The handler can optionally provide a return value to change the following in the payment dialog:

  • total
  • shippingAddress
  • shippingOptions
paymentRequest.onShippingOptionsChange(async (selectedShippingOption) => {
  const { newTotal, newShippingAddress, newShippingOptions } = await someAsyncOperation(
    total
    shippingOption,
  );

  return {
    total,
    shippingAddress,
    shippingOptions,
  };
});

Payment element builder

In order to request a payment, you need to create a UI element. The SDK provides a built-in PaymentElement UI builder, which allows you to create and configure the payment buttons.

Each payment button can be rendered individually as well.

The Swift Elements Builder allows you to attach an onSubmit handler, which will be called once the user clicks on one of the buttons rendered by it. Depending on the arguments passed during mount, it will render one or more buttons.

const buttons = swiftCheckoutClient.elements();
buttons
  .onSubmit((paymentEvent) => console.log(paymentEvent))
  .mount({
    paymentMethods: [{ id: 'apple_pay' }],
    container: document.querySelector('#express-checkout-container'),
  });

Rendering buttons for available payment methods

Once the UI and Payment Request are configured, you have to check the availability of Swift payment methods and mount them into the page.

The SDK checks several factors to determine if a given payment method is available:

  • Is the payment method available for the given merchant?
  • Is the payment method available on the browser?
  • Is the wallet/card ready to accept payment requests?

After checking if making payments is possible, render the payment element into a given placeholder as shown below:

paymentRequest.canMakePayment().then((isAvailable) => {
  if (isAvailable) {
    paymentRequest.availablePaymentMethods().then((paymentMethods) => {
      buttons.mount({
        paymentMethods,
        container: document.querySelector('#express-checkout-container'),
      });
    });
  } else {
    console.error('No payment method available!');
  }
});

Requesting payment authorization

The authorization dialogue is where the user will review the payment requested, select a payment card and a shipping address. Finally, they can authorize the payment request to be processed.

Using the payment element builder, configure it to show the payment authorization dialogue from the Payment Request instance upon the onSubmit event. Once the user authorizes the payment the show method will resolve a PaymentResponse containing details about the payment authorization.

buttons.onSubmit((paymentMethodEvent) => {
  paymentRequest
    .show(paymentMethodEvent)
    .then((paymentResponse) => console.log(paymentResponse));
});

To understand more about the PaymentResponse objects see Mozilla's official PaymentResponse - Web APIs documentation.

Processing an authorized payment request

To process a payment, the SumUp API requires you to create a checkout for a given amount. The checkout creation requires an authenticated request. Thus, we recommend implementing an endpoint on your backend that will authenticate with our API, create a checkout and return a checkoutId.

Once you obtain a checkoutId, call the processCheckout method from the SwiftCheckout client with the checkoutId and the PaymentResponse, which was received in the previous step, to start the processing the checkout.

paymentRequest
  .show(paymentMethodEvent)
  .then((paymentResponse) => {
    console.log(paymentResponse.details); // contactInfo, shippingAddress, etc.
    // here you create your order and a sumup checkout
    const checkoutId = 'c463bf5e-d397-4bca-9d2e-a4e04f668b1c';

    return swiftCheckoutClient.processCheckout(checkoutId, paymentResponse);
  })
  .then(console.log)
  .catch(console.error);

The complete implementation

const swiftCheckoutClient = new window.SumUp.SwiftCheckout(
  'fOcmczrYtYMJ7Li5GjMLLcUeC9dN',
);

const paymentRequest = swiftCheckoutClient.paymentRequest({
  total: {
    label: 'One Shoe',
    amount: {
      value: '100.0',
    },
  },
  shippingOptions: [
    {
      id: 'post',
      label: 'postal service',
      amount: { currency: 'EUR', value: '0.00' },
      description: 'free post',
    },
  ],
});

const buttons = swiftCheckoutClient.elements();
buttons.onSubmit((paymentMethodEvent) => {
  paymentRequest
    .show(paymentMethodEvent)
    .then((paymentResponse) => {
      console.log(paymentResponse.details);

      // Create your order and a checkout
      const checkoutId = 'c463bf5e-d397-4bca-9d2e-a4e04f668b1c';

      return swiftCheckoutClient.processCheckout(checkoutId, paymentResponse);
    })
    .then((result) => {
      if (result.status === 'PAID') {
        window.location.href = '/thankyou';
      } else {
        console.error(
          'It was not possible to process the checkout',
          result.message,
        );
      }
    })
    .catch((error) => {
      if (
        error instanceof SumUp.SwiftCheckout.Errors.PaymentRequestCancelledError
      ) {
        console.error('Cancelled by the user');
      } else {
        throw error;
      }
    });
});

paymentRequest.canMakePayment().then((isAvailable) => {
  if (isAvailable) {
    paymentRequest.availablePaymentMethods().then((paymentMethods) => {
      buttons.mount({
        paymentMethods,
        container: document.querySelector('#express-checkout-container'),
      });
    });
  } else {
    console.error('No payment method is available.');
  }
});

Error handling

The Swift Checkout SDK returns a series of Errors depending on the event that has taken place. You can use the errors to customise the user experience and communicate error causes as you see fit.

  • PaymentRequestCancelledError is thrown when the end user closes the open payment dialog or presses the button esc.

  • PaymentRequestInvalidActionError is thrown when the end user has submitted the payment dialog and then attempted to cancel the payment. Once the payment form is submitted the payment can no longer be cancelled.

  • PaymentRequestInternalError is thrown when attempting to handle the payment request in a forbidden manner. Reasons that you may receive include the following codes, available in the code field of the Error object:

    • SHIPPING_CONTACT_SELECTION
    • SHIPPING_ADDRESS_SELECTION
    • SHIPPING_METHOD_SELECTION
    • INTERNAL_VALIDATION
    • COMPLETE_PAYMENT
    • UNKNOWN

Apple Pay Setup

Prerequisites

Verify your domain with Apple Pay

To use Apple Pay, you need to register with Apple on all of your web domains which will show an Apple Pay button.

Apple’s documentation for Apple Pay on the Web describes their process of “merchant validation”, which SumUp handles for you behind the scenes. You don’t need to create an Apple Merchant ID, CSR and so on, as described in their documentation. Instead, follow the steps in this section:

  1. Request the domain association file through our contact form and host it at https://[YOUR_DOMAIN_NAME]/.well-known/apple-developer-merchantid-domain-association.

  2. Once hosted, request assistance from our integration specialists through the form, to register your domain with Apple.