The eBay Buy APIs (Marketing, Feed, Browse, and Order) are RESTful APIs that use OAuth authentication, JSON payloads, and eBay HTTP headers. They provide the capabilities you need to create an eBay shopping and buying experience in your app or website. You can use the eBay Buy APIs to build an application that displays eBay items and marketing information for these item, lets shoppers purchase their items, and lets you track and obtain details of the purchase orders. They also provide legacy IDs that enable you to use the Post Order API for returns and cancellations. See Post order tasks for details.
Shoppers can be guests or eBay members. With guest shoppers, the buyer is anonymous. For eBay members, the buyer is signed into eBay.
Several Buy API calls require the category ID. You can use the Commerce Taxonomy API to find the category for a call, to narrow the result set to categories in buyers' areas of interest, and minimize the number of unwanted items. For more information, see Get Categories for Buy APIs.