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Data
Meta Pixel
Meta's browser-side tracking tag, which fires from the visitor's browser and is therefore subject to ad blockers, ITP and ATT. Now normally paired with the Conversions API rather than used alone.
Why it matters
Pixel-only measurement has been structurally incomplete since ATT, and the loss is not random: it is concentrated in the iOS users many DTC brands over-index on.
In practice
Run it alongside CAPI with a shared event_id so the two deduplicate. Pixel alone understates; pixel plus CAPI without deduplication overstates.
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