Loss notification

A loss notification is the message an exchange sends to a bidder, by calling the bid's loss URL (lurl), to say that the bid lost and why, using a standard loss reason code.

The bidder supplies the URL in the lurl field of its bid. The exchange calls it when it knows the bid lost, filling in macros first. OpenRTB 2.6 lets exchange policy decide whether to send loss notices at all, and whether to reveal the clearing price; if not, ${AUCTION_PRICE} is left empty (IAB Tech Lab, OpenRTB 2.6, section 4.2.3).

The reason travels in ${AUCTION_LOSS}, using the list in OpenRTB 3.0. Code 100 means the bid was below the auction floor, 101 below the deal floor, 102 lost to a higher bid, 103 lost to a bid for a deal and 104 buyer seat blocked. Codes from 200 upward cover creatives filtered for reasons such as size, category or advertiser exclusions (IAB Tech Lab, OpenRTB 3.0, List: Loss Reason Codes). OpenRTB 2.6 added ${AUCTION_MIN_TO_WIN}, the lowest bid that would have won. Buyers use these signals to tune bid shading and to find creatives that exchanges keep rejecting.

Example: A DSP sets "lurl": "https://dsp.example/loss?r=${AUCTION_LOSS}&min=${AUCTION_MIN_TO_WIN}". It receives r=102&min=3.41 for a bid of $3.20, so it learns it lost on price by 21 cents. A run of code 209 instead would point to a category block, not price.

Related terms: nurl, burl, bid shading, bid response, floor price, OpenRTB.

Authoritative source: IAB Tech Lab, OpenRTB 2.6, section 4.2.3 field lurl and section 4.4 macros, with the OpenRTB 3.0 loss reason list (accessed 9 November 2026).

Read the full guide: OpenRTB 2.6 explained: bid request anatomy, field by field.