Event deduplication between client and server

When browser and server both report Purchase for the same checkout, ad platforms count it twice unless you explicitly deduplicate. Meta uses event_id. Google uses order_id or transaction ID in upload conversions. TikTok uses event_id.

The failure mode is common: engineering adds server-side tracking, marketing keeps the pixel, nobody coordinates IDs. Both paths fire independently with different identifiers.

Dedup is not automatic — you must design IDs at the business-event layer, not per transport.

Generate one ID at the moment of conversion — a UUID, your order ID, or a deterministic hash of transactionId + eventName. Pass it to both the browser capture and the server/edge delivery. Meta collapses matching events within its dedup window when event_name, event_time, and event_id align.

Use a stable ID tied to the business event, not a random value generated separately on client and server. transactionId works well for purchases; for SignUp, use a server-generated ID returned in the API response.

const eventId = `purchase_${order.id}`;

trackstack.capture("Purchase", {
  email: order.email,
  value: order.total,
  currency: "USD",
  transactionId: order.id,
  eventId,
});

Meta requires event_id on both pixel and CAPI events with matching event_name and close event_time for optimal dedup. Large time gaps reduce match confidence.

Google deduplicates on order_id in Enhanced Conversions and offline conversion uploads. GA4 ecommerce uses transaction_id with separate rules — do not assume one ID covers all Google surfaces.

TikTok Events API follows Meta-like event_id patterns. LinkedIn dedup is less documented — prefer a single authoritative delivery path or consistent timestamps.

Audit delivery logs for the same eventId with HTTP 200 on browser and server — that is expected. Flag the same transactionId with different eventId values — that is a bug.

Add code review rules: every conversion capture() includes eventId. Missing IDs are silent until ads manager shows inflated counts.

Document canonical events in Events so product and growth use the same names across SDK, docs, and dashboards.

Fire a test purchase with a fixed eventId from staging. Confirm one attributed conversion in Meta Test Events and one row per platform in TrackStack delivery logs.

Compare attributed conversions to billing for a 24-hour window after launch — not just pixel helper green checks.