gclid vs fbclid vs ttclid are three click ids, and none of them fills the others.

gclid is the query value, not the Conversion Linker cookie

The landing query parameter is gclid. The Conversion Linker cookie is _gcl_aw. That cookie string is not the upload field adIdentifiers.gclid. Pasting the cookie name, or the cookie blob, into the Google field sends a token Google did not issue as a click id. Read gclid from the landing URL and store that value.

http to https, apex to www, and locale prefixes that drop the query will eat gclid before the first page script runs. Preserve the log across redirects. A 302 that lands on a pretty URL is the usual paid-search incident. The Google linker parameter _gl stitches GA4 client_id across domains. It does not fill fbclid, and it does not fill ttclid, and a working _gl with a missing gclid is a screenshot where GA4 looks continuous and Google Ads does not.

Offline and enhanced-conversion uploads still need the click id or hashed user data. A CAPI-style event_time integer is not Google's conversionDateTime. Do not paste gclid into Meta because the Google row failed. Fix the Google field.

fbclid becomes fbc only in Meta's cookie shape

Meta's click cookie is _fbc, shaped fb.1.creationTime.fbclid. creationTime is Unix milliseconds, the landing time. event_time on the same payload stays in seconds. Dividing every timestamp by 1000 repairs event_time and forges fbc. Send the cookie value when you have it. If the cookie never existed, rebuild fbc from the stored fbclid and the landing time in milliseconds. A raw fbclid in user_data.fbc fails that shape.

You cannot invent _fbp. That random is the browser id the pixel minted. A new random per purchase is a new person. A constant is one fake browser for the shop. Omit fbp when you do not have the cookie. Do not hash fbp, fbc, fbclid, gclid, or ttclid. They are already opaque. Hashing them deletes the join.

Safari expires script-writable cookies in days. Persist fbclid server-side, keyed by a session you own, with a TTL past the click window you actually use, not past the cookie max-age. The thank-you page on another host will not see _fbc from the landing host unless you forward the id. Shopify and similar checkouts drop unknown query params unless the integration documents a passthrough.

ttclid stays on the TikTok body, in the clear

Store ttclid from the landing URL the same way you store fbclid. TikTok Events API uses it on web events. Without it, matching leans on hashed email and on plaintext IP and user agent. ttp is the _ttp cookie the pixel writes. You copy it. The server will not mint it. fbc is not ttp.

On Events API 2.0, ttclid rides on the web event inside the data array, next to event_source web and the Pixel Code on event_source_id. On the older pixel/track path it rides in context. A Meta user_data object posted at TikTok does not place it. App events are a different source and, on 2.0, allowlist. Do not copy a web ttclid onto an app body and call the click matched.

One landing request can carry gclid and fbclid and ttclid only if the user arrived from one platform. Usually one of them is present. Capture whichever keys exist. Do not require all three before you persist the one you have. A later purchase sends each id only to the vendor that issued it.

What each vendor actually wants

Three fields. A column named click_id that stores only gclid feeds one of them.

Google:  adIdentifiers.gclid = landing gclid   (not _gcl_aw)
Meta:    user_data.fbc = fb.1.<landing ms>.<fbclid>
TikTok:  ttclid from the landing query, plaintext, web events

The same pattern covers the click ids this page is not about

msclkid is Microsoft. li_fat_id is LinkedIn. twclid is X. Each is captured from the landing URL and sent only to the vendor that minted it. A warehouse column can hold all of them. A Meta user_data object should hold fbc and fbp, not the whole set. A TikTok web event should hold ttclid and, when you have it, ttp. A Google upload should hold gclid or gbraid or wbraid.

Hosted checkout is where the query dies. Put the ids you captured on the URL that leaves for checkout, or stash them server-side under a first-party session. Do not assume a platform will pass unknown parameters through. GA4's _gl linker is analytics stitching. It is not auto-tagging, and it is not a substitute for storing fbclid.

Validate per payload. A Meta body with a raw fbclid in fbc fails the fbc shape. A TikTok body with no ttclid can still be legal and weakly matched. A Google upload with the cookie blob in the gclid field is the wrong token even when the rest of the conversion is hashed correctly. Three checks, three artifacts.

What does not transfer

• gclid does not fill fbc or ttclid. fbclid does not fill gclid or ttclid.
• _gcl_aw is the Conversion Linker cookie. The upload field is the gclid query value.
• gbraid and wbraid are separate Google click ids, not decorations of gclid.
• utm_source is not a click id. A pretty URL that dropped gclid still has a UTM story and no Ads join.
• fbc is fb.1 plus milliseconds plus fbclid. The middle number is not event_time.
• Do not hash click ids. Do not invent _fbp.
• Persist each id server-side. Safari will drop the cookie before a long purchase cycle.

Sources

• Google Ads: About auto-tagging
• Meta: fbp and fbc
• TikTok: Events API 2.0 track

Contract pages

The dated argument is above. These pages are the field lists.

• Click ids
• The _fbc cookie
• Cross-domain measurement