Full Answer

The core mechanism is straightforward: your client-side Pixel fires a purchase event with an event ID like order_12345, and your server sends the same purchase event to the Conversions API with the same event ID. Meta's ingestion pipeline matches them within a 48-hour window and collapses them into a single attributed conversion. The same principle applies to Google Ads Enhanced Conversions and TikTok Events API — each platform has its own deduplication key, but the logic is identical.

The danger of skipping deduplication is not just inflated numbers. Double-counted conversions feed false signals into automated bidding. The algorithm sees twice the conversions at what appears to be half the cost per acquisition, so it bids more aggressively on audiences and placements that may not actually be converting. PixelFly's 2026 analysis found that stores without proper deduplication routinely overstated Meta-attributed revenue by 20 to 40 percent, leading to misallocated ad spend that only surfaces when reconciled against actual bank deposits.

Implementation requires generating the event ID at the point of conversion — typically the thank-you page or order confirmation — and passing it to both the Pixel's dataLayer push and the server-side API call. The ID must be deterministic (derived from the order number, not randomly generated per request) so both channels produce the same value. For stores running multiple destination pixels alongside server-side tracking, consistent event IDs across every channel become the single most important piece of tracking infrastructure to get right.