Aggregated Event Measurement: What Still Applies in 2026

What Aggregated Event Measurement Is

Aggregated Event Measurement (AEM) is Meta's framework for measuring conversions from iOS 14+ users who have opted out of tracking under Apple's ATT framework. Rather than individual-level attribution (knowing exactly which ad a specific user clicked before purchasing), AEM uses aggregated and modelled data at the campaign level.

The key constraint: only 8 conversion events per verified domain can be used for ad optimisation targeting iOS users. These must be prioritised in order of importance.

AEM Requirements That Still Apply in 2026

1. Domain Verification

Your domain must be verified in Meta Business Manager to use AEM. If your domain is not verified, conversions from iOS users cannot be attributed to your campaigns.

Verify at: Business Settings → Brand Safety → Domains → Add domain. Add the DNS verification TXT record or upload the verification HTML file.

2. 8-Event Limit and Prioritisation

In Events Manager → Aggregated Event Measurement → Configure Web Events, you see your 8 available event slots. Configure them in priority order:

• Slot 1 (highest priority): Purchase — your primary conversion event
• Slot 2: Lead — form submissions, sign-ups
• Slot 3: InitiateCheckout / begin_checkout
• Slot 4: AddToCart
• Slot 5: ViewContent / view_item
• Slot 6-8: Other events relevant to your funnel

For iOS users, only the highest-priority completed event in a session is reported. If a user adds to cart AND purchases, only the Purchase is counted (not AddToCart). This is why Priority 1 must be your most important conversion event.

3. Shortened Attribution Windows

For iOS, the attribution window is 7-day click or 1-day view — the 28-day click window no longer applies to iOS. This means purchases made more than 7 days after clicking your ad are not attributed on iOS.

4. Modelled Data

Meta uses statistical modelling to estimate conversions from iOS users who cannot be tracked. Your campaign reports include a mix of measured and modelled conversions — Meta does not separate them in the standard reporting interface.

What CAPI Improves Within AEM

Conversions API improves AEM performance by providing more conversion signals that Meta's model can learn from. More real conversion data → better modelling of estimated conversions → higher-quality data for the 8-event optimisation signals.

CAPI does not remove the 8-event limit or restore the 28-day attribution window — the AEM constraints are Apple-imposed and meta cannot change them. CAPI improves the quality of data within those constraints.

Summary

AEM continues to apply in 2026 for iOS users: domain verification required, 8-event limit with priority order, 7-day attribution window, and modelled conversion data. Configure your 8 event slots with purchase as priority 1. CAPI improves your data quality within AEM constraints but cannot remove Apple's framework limitations. Ensure domain verification is in place before any advertising campaign relies on iOS conversion tracking.

See our Facebook CAPI Setup service for AEM configuration.

Need AEM and CAPI configured correctly? Contact Adslytics.