RTBlintAlpha
nbr 14: Ads.cert Authentication Violation
What it means
The ads.cert signature failed verification.
A bidder returns nbr on an otherwise empty BidResponse to say why it is not bidding, instead of (or alongside) an HTTP 204. Code 14 is ads.cert authentication violation.
What to do about it
The bidder could not verify the seller through ads.txt or ads.cert. Check that your ads.txt is reachable and lists the seller account exactly as the request declares it, and that the sellers.json entries the schain references resolve. These codes are the buyer telling you your trust chain does not check out.