Conversion ID
A conversion ID is a unique identifier your systems generate for one distinct conversion and attach to every copy of that conversion - pixel event, server event, CRM upload - so the ad platform's deduplication collapses the copies into one counted conversion. One real purchase must have exactly one ID on every path that reports it; two IDs mean two conversions, one shared ID means one.
Which field carries it on each platform
| Platform | Field | Dedup behavior |
|---|---|---|
| Meta | event_id | Paired with an identical event_name across pixel and server; duplicates drop within a 48-hour window, the first copy received wins |
| TikTok | event_id | Pixel and Events API events deduplicate on a shared event_id within 48 hours; mismatched IDs double-count, colliding stale IDs silently drop real conversions |
conversion_id | Recommended method: passed in metadata from both pixel and server; an hourly deduplication job keeps the higher-quality event | |
event_id | Passed when the tag or an MMP and the Conversions API both report the same event | |
| Snapchat | client_dedup_id | Must be identical across pixel, App Ads Kit, and API; honored within 48 hours of the first occurrence |
Snapchat additionally separates transaction_id for order-level identity, which in a tracker funnel is naturally the tracker's transaction identifier.
How to generate one that survives the whole funnel
Reddit's own guidance gives the two schemes: a stable business identifier such as an order number for purchases, or a hash of the timestamp, event type, and key parameters for events without one. The property that matters is determinism: the browser side and the server side must be able to compute the same value for the same conversion without talking to each other. An ID that only one side can generate silently disables deduplication - both copies count, and the error surfaces later as inflated numbers.
The failure mode runs in both directions. Reddit warns that reusing one ID across too many events marks real conversions as duplicates and costs attribution, while two different IDs for one conversion produce exactly the double-counting the field exists to prevent.
Conversion ID versus event ID deduplication
The mechanics of how platforms compare, keep, and drop copies are covered separately in event ID deduplication. The division of labor: you own the ID scheme, the platform owns the dedup window - 48 hours on Meta, TikTok, and Snapchat, an hourly job on Reddit that only processes events that arrived within two days. A working setup needs both halves: a deterministic scheme and every channel actually sending it.