What Is Aggregated Event Measurement (AEM)?

AEM prioritisation in an ecommerce account

A DTC store verifies its domain and configures 8 events: Purchase (priority 1), InitiateCheckout (2), AddToCart (3), ViewContent (4), Lead (5), and three custom conversions (6 to 8). An iOS opt-out user views a product, adds to cart, and buys. Meta receives only Purchase because it is the highest priority that fired. Skipping AEM setup leaves the account defaulting to Meta's guess, usually the wrong 8, and Purchase optimisation quietly underperforms.

Benchmarks

• Event cap: 8 per verified domain (2 slots reserved for value optimisation on the top event).
• iOS opt-in rate globally: roughly 25 percent in 2026, lower on privacy-heavy regions.
• Reporting delay for AEM events: 24 to 72 hours (vs near-real-time for opted-in).

Why it matters

AEM is the ceiling on Meta optimisation for iOS opt-out traffic, which is still 60 to 75 percent of Apple's user base. A misconfigured priority order silently starves the algorithm; buyers see soft CPA drift with no obvious cause.

Common mistakes

• 1.Leaving AEM on Meta defaults. Priority 1 may not be your money event.
• 2.Skipping domain verification. AEM cannot activate without it and iOS attribution collapses.
• 3.Using all 8 slots on soft events (ViewContent, engagements). Purchase gets deprioritised.
• 4.Frequent reshuffles. Every priority change triggers a 3-day event delay.

FAQs about Aggregated Event Measurement