The Offer API provides the ability to place and retract a proxy bid for a buyer and to retrieve all the auctions where the buyer is bidding.
Note:
This is a 
(Limited Release) API available only to select developers approved by business units. For information on how to obtain access to this API in production, see the Buy APIs Requirements.
Technical overview
The Offer API has the following main objects:
- auction - A buying option where buyers bid against each other in order to win the auction and purchase the item. There are two buying options; auction and fixed price (Buy It Now). Items can have one of these options or both. If an item offers both buying options, after the first bid is placed, the Buy It Now option is removed and the item is sold to the highest bidder.
- proxyBid - A bid placed on behalf of a buyer on an auctioned item.
Business use cases
This section outlines the high-level use cases using the Offer API.
Place a proxy bid
You can place a bid (proxy bid) for an auction item on behalf of a buyer.
Retrieve an auction
You can retrieve bidding details that are specific to the buyer for an auction where the buyer has placed a bid.
API restrictions
Please note the following constraints for the Offer API.
Item identifier incompatibility
The Buy APIs identifiers of items do not match the identifiers used on the eBay site. So you cannot use the Buy APIs RESTful item identifiers with any of the eBay legacy APIs, such as Finding. But if you have the legacy item identifier, you can find the RESTful item identifier using the Browse API getItemByLegacyId method.
Regional/site constraints
For a list of the supported eBay sites for all the Buy APIs, see Buy API Support by Marketplace.
To specify the site, set the X-EBAY-C-MARKETPLACE-ID request header to the site. For example:
X-EBAY-C-MARKETPLACE-ID = EBAY_GB
eBay Buy API requirements
Although the eBay Buy APIs are available for anyone to use in eBay's sandbox environment, use of the APIs in production is restricted. Users must meet standard eligibility requirements, get approvals from eBay support organizations, and sign contracts with eBay to access the Buy APIs in production. See Production eligibility requirements for information about production access.
Rate limits
The Offer API limits the number of calls that can be made per day on behalf of your application. For the current application rate limits, see the eBay API Call Limits page.