Mock sample for your project: Jumpseller API

A product library is a representation of all the items that can be
displayed, put in a shopping cart and sold to a customer. Items may be
either producs or discounts.
A product is a synthetic construct, wrapping one or more variants (which is
the actual item being sold) Variants expresses different variations of
properties such as for example price, size or color. A discount will reduce
the total amount charged in a shopping cart. It can be used per item line,
or on the whole cart. It may reduce the affected amount by a percentage, or
by a fixed amount.
Together, the above types of entities makes up a complete library. The
library can be fetched as a whole through the library endpoint, where each
consecutive change applied to the library is available. Once the full
library is retrieved, only later events needs to be fetched to keep the
client up to date with the server
All path patterns "/organizations/{organizationUuid}/" can be replaced
with "/organizations/self/" for convenience as all endpoints are for
authorized users.

The Metadata API has operations that retrieve configuration details pertaining to the different eBay marketplaces. In addition to marketplace information, the API also has operations that get information that helps sellers list items on eBay.

Please make sure you use the correct version of the APIs for your use case. To find out the appropriate version, go to the API Docs drop down on the menu.

Use the Fulfillment API to complete the process of packaging, addressing, handling, and shipping each order on behalf of the seller, in accordance with the payment method and timing specified at checkout.

The Charity API allows third-party developers to search for and access details on supported charitable organizations.

reverb

The Negotiations API gives sellers the ability to proactively send discount offers to buyers who have shown an "interest" in their listings. By sending buyers discount offers on listings where they have shown an interest, sellers can increase the velocity of their sales. There are various ways for a buyer to show interest in a listing. For example, if a buyer adds the listing to their Watch list, or if they add the listing to their shopping cart and later abandon the cart, they are deemed to have shown an interest in the listing. In the offers that sellers send, they can discount their listings by either a percentage off the listing price, or they can set a new discounted price that is lower than the original listing price. For details about how seller offers work, see Sending offers to buyers.

The Recommendation API returns information that sellers can use to optimize the configuration of their listings on eBay. Currently, the API contains a single method, findListingRecommendations. This method provides information that sellers can use to configure Promoted Listings ad campaigns to maximize the visibility of their items in the eBay marketplace.

One API serving data spanned across multiple verticals