The payment sheet is the most important user-facing aspect of the Apple Pay experience. Also, this is where the user should spend the least amount of time. Your app convinced the user to purchase the product. The payment sheet is where you will take the user from desire to acquire in as few taps as possible, two taps being the ideal.
In the previous chapter, you learned how to present information in the payment sheet, including a list of the shipping methods you can make available to your customers, and the total price of the order. With the payment sheet up, the user can change the shipping type (from delivery to store pickup, for example), the shipping address, and the payment method (the payment card that will be used to fund the transaction). For each change the user makes, you must update the payment request's summary items to reflect it. For example, when the user changes the shipping method, you must update the summary item that displays the...