${AUCTION_MIN_TO_WIN}
What it expands to
Minimum bid needed to win (or to tie the winner), same currency and units as the bid.
Expands in win and loss notices with the minimum bid that would have won (or tied) the auction, in bid currency and units. Added in 2.6.
What to watch for
This is the input bid-shading models are built on. In a win notice it tells you how much you overpaid; in a loss notice, how far off you were. Treat an exchange that sends it as giving you free price discovery.
Encoding
When a macro rides inside another URL as a query parameter, the expanded value must survive URL parsing: exchanges support suffixed forms like ${AUCTION_MIN_TO_WIN:B64} (base64) where documented, and values containing reserved characters must be percent-encoded. An unencoded expansion is the most common reason a notice URL truncates at the first ampersand.