Full Answer

iOS 14.5's App Tracking Transparency (ATT) prompt allowed users to block Facebook's IDFA identifier, stripping the Pixel of the data it needs to match ad clicks to purchases. CAPI bypasses this entirely by sending conversion data from your server directly to Meta's API with no browser involvement. The Pixel captures what it can; CAPI fills the gaps with server-side event data.

WooCommerce stores implement CAPI by connecting an order completion hook to a server that POSTs the purchase event with hashed customer identifiers (email, phone, IP address). Facebook uses these to match the conversion back to an ad click even without IDFA. Running Pixel and CAPI together with deduplication enabled consistently outperforms Pixel-only attribution in iOS-heavy markets, particularly for US and European audiences where ATT opt-out rates are highest.