Sometimes a store will not be able to fulfill your order and you will be able to see the option to update your items in the app. You have 10 minutes to choose a new item or continue without the item, or your order will be canceled. You can also choose to cancel your order at that time.
The item that is no longer available will be displayed and you can choose to modify it or continue without it. You will then see a new payment screen and can consult it before re-validating your order.