Click ID
A click ID is a platform-specific parameter appended to your landing page URL when a user clicks an ad - fbclid on Meta, ttclid on TikTok, rdt_cid on Reddit, ScCid on Snapchat - and it identifies that exact click. When a server event carries the same click ID, the platform can attribute the conversion to the ad without relying on cookies or probabilistic guessing.
Why click IDs get lost
The click ID lives in the URL, so every hop that rewrites the URL is a chance to lose it: an affiliate network redirect, a tracker that masks the offer URL, a landing page that forwards to a second domain. The platform attaches it exactly once - at the ad click - and never re-attaches it downstream. A funnel that does not capture the parameter on the first landing page cannot recover it later, and the server event goes out without its strongest identifier.
How to carry it into server events
The working pattern has three hops: the landing page or tracker stores the click ID at click time; the tracker returns it with the conversion postback; the delivery layer maps it into the platform's field. The field names differ by platform: click_id on Reddit and Snapchat, ttclid on TikTok, and on Meta the fbc parameter, which wraps fbclid in the fb.1.<timestamp>.<fbclid> format. Reddit additionally extracts a click ID found in event_source_url as a fallback when the dedicated field is missing.
The full mechanics - which hops lose which parameters, and how to wire a tracker so nothing drops - are covered in link tracking and click ID loss. On match quality, the click ID is the one key Reddit and Snapchat rank first; how it compares with hashed identifiers is in match key.