rdt_cid: The Reddit Click ID From Ad Click to CAPI Payload
The Reddit click id - rdt_cid in the landing URL - is the identifier Reddit appends the moment someone clicks a Reddit ad, and it is the strongest match key a Reddit conversion event can carry, because it ties the conversion to one exact click rather than to a hashed guess. Reddit strongly recommends passing it with every server event; the hard part is not sending it, it is still having it by the time the conversion fires. This guide follows rdt_cid through the whole funnel: where it appears, where it disappears, and the chain that hands it to the CAPI payload.
Where rdt_cid Comes From
When a user clicks a Reddit ad, the destination URL arrives with rdt_cid in its query string - a long numeric identifier for that exact click. Reddit attaches it once, at the click, and the parameter has no downstream lifecycle of its own: every redirect after the landing page is your pipeline's responsibility. The platform's own payload sample shows the value both as a standalone click_id field and living inside event_source_url - the two places a conversion event can carry it.
That single-attachment rule is why link tracking and click ID loss treats Meta's fbclid and TikTok's ttclid with such care. rdt_cid behaves the same way, and so do the failure modes: one URL rewrite that drops the query string severs the attribution chain without any error.
Where Redirects Lose It
A typical tracked funnel passes the landing URL through several rewrites: the affiliate network's redirect, the tracker's click wrapper, a masked offer URL, sometimes a second landing on a different domain. Any rewrite that reconstructs the URL instead of preserving its query string silently discards rdt_cid. No error appears anywhere - conversions simply stop carrying their strongest identifier, and the first symptom is a match rate that sags in Reddit's event diagnostics.
The practical defense is capture-at-landing: store the click ID the moment the visitor arrives, before any later hop gets a chance to rewrite it away.
Three Hops Into the CAPI Payload
| Hop | What happens to rdt_cid |
|---|---|
| 1. Landing page | The parameter arrives in the URL; capture it into the tracker's click/session record immediately |
| 2. Tracker | The click ID is stored against the visitor; when the conversion fires, the tracker returns it with the postback |
| 3. Delivery layer | The postback value maps into the CAPI event's click_id field - or stays in event_source_url, which Reddit parses as a fallback |
Reddit's payload supports both placements: a dedicated click_id field at the top level of the event, and automatic extraction of a click ID found in event_source_url when the dedicated field is missing. The explicit field is the reliable one - the fallback only works while the URL survives intact through the funnel. As a match key, the click ID sits at the top of Reddit's recommendations alongside the IP address; the full matching picture is in match keys.
For a tracker-based funnel this chain is exactly what a delivery automation runs: one postback in, rdt_cid mapped to click_id, hashing and deduplication handled per network - which is the job MOST performs for Reddit alongside Meta, TikTok, Pinterest, and Snapchat. To test a single event by hand, Pixel Activator sends valid Reddit conversions without any setup; the credentials it needs are covered in Reddit Conversions API setup, and the payload side - fields and windows - in Reddit conversion events and the complete guide.