Apple has made it very clear that in order to transmit the necessary data (IDFAs or other metadata for probabilistic matching) from your app necessary for attribution of a specific user to an ad, you must gain consent via ATT.
This policy also applies to a publisher app sending that same data (IDFAs, or other metadata for probabilistic matching), but Apple considers publisher websites out of the scope of ATT.
That means that for app-to-app ads, the user has to consent via ATT in both apps. While there is no ATT equivalent on the web, the user still needs to opt in via ATT in the advertiser’s app in order to attribute a web-to-app ad conversion.
Unfortunately, since SKAdNetwork is not compatible with mobile web inventory, there is not currently an Apple-approved way to attribute a web-to-app conversion if a user does not opt in via ATT in the advertiser’s app. We're aware this is a major problem, and we're hoping Apple will clarify their intentions.
Updated about 1 year ago