BidResponse object
BidResponse is the top-level object a bidder returns to an exchange. It echoes the request ID, groups bids by buyer seat in BidResponse.seatbid, names the currency of every price, and can explain a no-bid with a reason code.
How it is used
A bidder that passes can return HTTP 204 with an empty body, the cheapest option, or a BidResponse holding only BidResponse.id and BidResponse.nbr to say why. A response with neither seat bids nor a reason gives the exchange nothing to act on. Exchanges match responses to auctions through the echoed ID, so a response with the wrong ID cannot be matched.
The Bid response anatomy page covers it in more depth.
Fields
Where it sits
Contains: SeatBid.
All objects
The field reference index lists every OpenRTB 2.x object.