If the bid request has a placement count (“plcmtcnt”) greater than 1, then the implication is that the bidder is submitting bids to a Generalized Second Price auction where multiple identical placements are being offered in the same content feed or stream.
Example If a bid request is for 5 ad placements within a feed based layout. The bidder can return 1-5 bids. The exchange runs a generalized second price auction across these bids. The bidder can potentially win between 0-5 placements in the auction.
An example bid response would look like
{
"id": "1234567890",
"seatbid": [{
"bid": [{
"id": "1",
"impid": "1",
"price": 10,
"nurl": "http://adserver.com/WinNoticeUrlThatReturnsNative1",
"adm":"<native response>"
},
"bid": [{
"id": "2",
"impid": "1",
"price": 20,
"nurl": "http://adserver.com/WinNoticeUrlThatReturnsNative2"
"adm":"<native response>"
}]
}]
}