What is Aggregated Event Measurement (AEM)? — Meta Ads Glossary — details
Aggregated Event Measurement is Meta's protocol for measuring web conversion events from users who have limited tracking via Apple's App Tracking Transparency, aggregating data in a privacy-preserving way rather than tracking individuals. Each verified domain can configure and prioritize up to 8 conversion events, and only the highest-priority event that occurred is reported per user session.
Because only 8 events per domain get full measurement under AEM, agencies configure event priority carefully — typically ranking purchase above add-to-cart above page view — so the most business-critical event is the one guaranteed to be captured and reported for optimization, rather than losing signal on a lower-value event that happened to occur later in a session.
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