Aggregated Event Measurement (AEM)
Aggregated Event Measurement is Meta's post-iOS-14 framework for tracking conversions in a privacy-compliant way. AEM lets you prioritize 8 events per domain in order of importance and sends a privacy-aggregated signal back to Meta's optimizer.
iOS 14.5 broke direct user-level tracking by requiring explicit opt-in. AEM is Meta's workaround: instead of attributing every conversion to a specific user, AEM batches data and reports it with a delay and at a coarser granularity.
For FE, the typical AEM event priority is: Lead (highest), CompleteRegistration, InitiateCheckout (if you have calendar booking), then PageView at the bottom.
AEM only matters for landing-page conversion campaigns, not native lead form ads. Lead form ads use Meta's native lead-tracking and are not affected by AEM in the same way.