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Likely cause: Deduplication differences. Upstack and destination platforms use different deduplication keys. Upstack deduplicates by event_id before forwarding, but the destination may further deduplicate by user + event type + time window. How to reconcile:
  1. A gap of 5–10% is normal and expected due to deduplication differences.
  2. Check Upstack’s Live Event Stream — if you see duplicate event_id values, your pixel may be firing the same event multiple times (see Duplicate purchase events).
  3. For Meta specifically: if you send both browser pixel events and Upstack server events for the same conversion, Meta deduplicates them using event_id. Ensure your Upstack events include the same event_id as the browser pixel fires.
  4. For Google Analytics: GA4 automatically deduplicates events with the same event_name, event_timestamp, and user identifiers within a short window. This means GA4 may show fewer events than Upstack.
  5. To reduce discrepancies, ensure deduplication keys are consistent across your pixel and Upstack’s server-side events.
Still stuck? Contact support@upstackdata.com with your Pixel ID and a description of the issue. We typically respond within a few hours.