For many years, the Meta Pixel handled most conversion tracking. It recorded activity in a visitor's browser and sent that information to Meta. Changes to browser privacy and Apple's App Tracking Transparency reduced how much data the Pixel could collect on its own. Conversions API, commonly called CAPI, helps recover some of that missing information by sending events from the advertiser's server directly to Meta. It does not replace the Pixel. The strongest setup uses both methods so the same purchase or lead can be recorded in the browser and on the server. To prevent one action from being counted twice, both versions of the event must use the same event ID. Meta can then identify them as one conversion. Cometly's comparison of the two methods reports deduplication rates above 80% for core conversion events when both systems are configured correctly. This additional source of data is particularly important for traffic from Apple devices. Browser tracking may miss conversions when cookies or scripts are blocked. As WeTracked explain, CAPI allows purchase information to reach Meta even when the Pixel cannot send it from the browser. Pixel and CAPI should be configured before the first campaign begins. It is much easier to confirm that events and IDs match before money is being spent than to investigate gaps after performance reports become unreliable. bm2500 offers a straightforward guide to the setup order.