Attribution Window Mismatch
Google Ads uses a 30-day click attribution window by default. Meta's default is 7-day click, 1-day view. GA4 operates on session-based attribution, not click-based. When a user clicks a Google ad on day 1, a Meta ad on day 10, and converts on day 12 — Google claims it (30-day window), Meta claims it (within 7 days), and GA4 attributes it to whichever source triggered the final session. Three platforms, one conversion, three claims.