Aggregated Event Measurement

Aggregated Event Measurement is Meta's post-ATT framework that limits each website domain to a set number of prioritized conversion events, commonly cited as eight, and reports them in an aggregated, privacy-preserving, delayed way.

You noticed after Apple's tracking prompt that your conversion numbers went strange, and this framework is a big reason why. When someone on iOS opts out of tracking, Meta can no longer measure their journey freely, so it falls back to Aggregated Event Measurement. Each domain gets a limited set of events, usually eight, and you rank them in order of importance. For opted-out users, only those ranked events count, and the data comes back grouped together and on a delay rather than person by person in real time.

So you sit down and decide which eight events actually matter, from a top-of-funnel view all the way down to a purchase, and you put them in priority order. That ranking quietly governs what you can measure and optimize toward for a meaningful slice of your iOS audience.

The honest catch is that ranking them wrong quietly costs you. For anyone who opted out, events below your priority list simply do not register, so if you bury your true money event under softer ones, you lose measurement on exactly the thing you care about most. This is a hard constraint on iOS, not a suggestion, and reshuffling the order can trigger a cooldown before it takes effect, so you cannot fiddle with it daily. Verify your current event count in Events Manager, since the number can change, and set your priority to match what actually pays you.

On iOS you only get to measure what you ranked, so rank the sale first and everything softer after.