Full Answer

Meta's one-click Conversions API is a simplified server-side tracking setup that WooCommerce stores can activate directly from the Meta Commerce Manager. It creates a parallel event pipeline alongside any existing CAPI integration — and therein lies the problem.

A WooCommerce store that already runs a CAPI plugin (whether PixelYourSite, a custom server-side integration, or a pipeline like Transmute Engine) is already sending server-side events to Meta. When one-click CAPI is enabled on top of this, Meta's servers receive two independent event streams for the same user actions. A single purchase generates two purchase events. A single add-to-cart generates two add-to-cart events.

Meta's deduplication system is designed to handle this — but only when both event streams use the same event_id for the same action. The event_id is a unique identifier attached to each event that tells Meta's server to count the two incoming records as one conversion rather than two. The problem is that one-click CAPI and third-party plugins generate their own event IDs independently, with no shared coordination. Unless both systems produce identical event_id values for the same user action, Meta treats them as separate events.

The result is conversion inflation. Ads Manager reports double the actual conversions, cost-per-acquisition appears half its true value, and Smart Bidding algorithms optimise against inflated signals — leading to budget misallocation. The fix is simple but absolute: run one CAPI integration, not two. If the existing plugin is functioning correctly with proper event coverage and deduplication, do not enable one-click CAPI. If switching to one-click, fully disable the existing plugin first.