Our goal is to make upgrading to Express Checkout as simple as possible for existing Afterpay merchants. There are no new APIs. The only changes you need to make to your existing Afterpay integration are:

  1. Add Express Checkout button to the cart and/or product pages and configure JS with Afterpay provided key

  2. Update the Create Checkout and Auth (or Capture Full Payment if using the Immediate Payment Flow) API call payloads

  3. Display the Afterpay Checkout Widget on a review page to enable dynamic updates to the order total after the Express Checkout flow (optional with Integrated Shipping)