Aggregated Event Measurement (AEM)

The Aggregated Event Measurement (AEM) is a protocol from Facebook to measure conversion events in iOS / iPadOS. It is based on Apple's Private Click Measurement (PCM) and offers similar restrictions:

  • A maximum of 8 conversion events are available (per domain)
    (when using Value Optimization, 4 of them are apparently already occupied)
  • The attribution window is a maximum of 7 days (from the ad click to the conversion)
  • If the app user has not consented to the tracking for the consent banner, only one conversion can be measured - this is where the prioritization of the events comes into play (see below)
  • There may be delays in tracking the conversion events of up to 3 days
  • The use of several Facebook pixels (within a domain) could be problematic

Prioritization of Conversion Events

Prioritization of the events is necessary due to the iOS restrictions and comes into play if an iOS user prohibits tracking:

In the case the user denied the tracking, only one conversion event can be measured. Facebook then selects the one that is highest in the prioritization list.
Depending on the website type, the purchase event should be at the top, followed by InitiateCheckout and/or AddToCart, then ViewContent etc.
After changes to the prioritization, it may take a few days for tracking to start again.

Instructions on how to set up conversion events on Facebook can be found here: