Full Answer

The gap between Facebook and GA4 conversion counts is one of the most common reporting frustrations for WooCommerce store owners, and it has three distinct causes that compound on top of each other.

The first cause is view-through attribution. Facebook counts a conversion when a user purchases within 1 day of seeing an ad impression, even if they never clicked. GA4 has no visibility into ad impressions — it only tracks sessions. If a user sees a Facebook ad, then later navigates directly to the store and purchases, Facebook claims the conversion and GA4 attributes it to direct traffic. The conversion count is the same (one purchase), but the attribution is completely different.

The second cause is attribution model differences. When a user clicks a Facebook ad, then later clicks a Google search result and purchases, both platforms claim the conversion. Facebook credits the original ad click within its 7-day window. GA4 credits the Google search as the last click. If you look at GA4 alone, Facebook appears to have driven zero conversions for that user.

The third cause is data loss. GA4 depends on the gtag.js script loading and executing in the user's browser. Ad blockers prevent this for an estimated 25-40% of traffic. Safari ITP restricts cookie lifetimes, causing GA4 to lose returning-user attribution. Consent banners delay or block tag execution. Facebook's Conversions API, implemented server-side, is immune to all three of these client-side failures because it sends data from the server, bypassing the browser entirely.

The practical result: Facebook's count is typically higher because it captures more (view-through, multi-touch) and loses less (server-side delivery). GA4's count is lower because it captures less (last-click only) and loses more (client-side failures).