The Checkout API makes it possible to purchase products from a Shopify store programmatically. A checkout in Shopify is the object used to manage a customer’s cart as it transitions to a paid checkout. This includes calculating taxes, shipping rates, attaching the customer’s information, and finally completing a purchase by submitting a payment. Use this API if you want a fully customized checkout user experience, while taking full advantage of the commerce engine used to power every Shopify store.