When iOS 27 was released, a legit advertising company found it could no longer serve ads to the Safari browser. This block appears to be a mistake on Apple's side, but the ad industry is up in arms about the implications.
Apple introduced App Tracking Transparency back in 2021 in order that users had to choose to allow ad companies to track them using identifiers. After a heavy initial impact, though, the rates of users allowing tracking has risen again, and advertisers have found alternative ways to learn about users.
However, according to advertising trade journal AdExchanger, The Trade Desk ad agency was blocked in iOS 27 by Apple itself. It appears that Apple is intentionally blocking data brokers who sell on tracked data, but in doing so it prevented The Trade Desk serving ads. The Trade Desk filed a bug report that surmised that the "intent seems to be to hard block domains that power 'post-cookie' identity." However, the affected addresses include the company's "ad request and delivery domain, not identity [tracking]."
This is the system where The Trade Desk, or any other vendor like Google, bids on ad space in real-time as a page loads for the user. If it wins that bid, the company then serves an ad to the web browser based on what the ad vendor thinks it knows about the viewer. This is not in itself about tracking individual users.
So far this sounds like a mistake on Apple's part, and that appears to have been backed up by how the block on The Trade Desk has effectively been removed. However, it is only removed in iOS 27.2, which so far is solely in beta testing. That means The Trade Desk still cannot serve ads to Safari, and will remain blocked from doing so until iOS 27.2 ships.
Source: AppleInsider · Summarized by HeadlinesBriefing