What does "First user CM360 advertiser name" mean in GA4?

It's the user-scoped version of the CM360 advertiser dimension — the advertiser whose CM360 ad first brought that user to your site. The unprefixed "CM360 advertiser name" is session-scoped and reflects the ad that drove the specific session instead.

What's the difference between "First user CM360" and "CM360" dimensions?

Scope. "First user" dimensions are user-scoped and attributed to the user's first touch; the unprefixed versions are session-scoped. Both are correct — they answer different questions, and mixing them in one report is why numbers often fail to reconcile.

Why are my GA4 CM360 dimensions showing (not set)?

Most often the CM360-to-GA4 link isn't configured (or is on a different property), or Floodlight tags aren't firing. It's also legitimately (not set) for any session with no CM360 exposure — organic, direct and non-CM360 paid traffic included.

Which CM360 dimensions are available in GA4?

Advertiser, campaign, placement (including placement cost structure) and creative (name, ID, type, type ID, version, format), plus CM360 source/medium — each available in both user-scoped "First user" and session-scoped variants.

Will CM360 dimensions backfill after I set up the link?

No — they populate from when the link is active onward, so date ranges before the link was configured will show (not set).

Concepts

GA4's CM360 dimensions explained: "First user" vs session scope, and why they show (not set)

TL;DR

When Campaign Manager 360 is linked to GA4, a set of CM360 dimensions appears in your reports — advertiser, campaign, placement, creative, each in two variants. The naming is where people get stuck: "First user CM360 advertiser name" and "CM360 advertiser name" are not the same dimension, and picking the wrong one quietly changes what your report means.

The scope distinction that trips everyone up

Prefix	Scope	What it answers
`First user CM360 …`	User-scoped, first touch	Which CM360 ad first brought this user to the site, ever
`CM360 …` (no prefix)	Session-scoped	Which CM360 ad drove this particular session

Mixing them in one report is the most common source of numbers that don't reconcile. A user acquired months ago by one campaign can have sessions attributed to a different one — both dimensions are correct, they're answering different questions.

What each dimension family covers

Advertiser — advertiser name and advertiser ID, the top of the CM360 hierarchy.
Campaign — campaign name and campaign ID.
Placement — placement name, placement ID, and placement cost structure (how the placement was bought).
Creative — creative name, creative ID, creative type, creative type ID, creative version and creative format.
Source / medium — the CM360 source/medium pairing, in both user and session scope.

Every one of these has both a "First user" (user-scoped) and an unprefixed (session-scoped) variant — so in practice you're choosing along two axes: which entity, and which scope.

Why they show (not set)

This is the other half of the search traffic these dimension names attract, and it usually comes down to the link rather than the dimension.

The CM360 ↔ GA4 link isn't configured, or was configured on a different property than the one you're reporting on.
Floodlight tags aren't firing on the pages in question, so there's no CM360 exposure to attribute.
The session had no CM360 exposure at all — organic, direct and non-CM360 paid traffic will legitimately be (not set) on these dimensions. This is correct behaviour, not a bug.
You're looking at a date range before the link existed. These dimensions don't backfill.

Using them without living in the UI

The practical problem with these dimensions isn't understanding them once — it's that reconciling CM360's own numbers against GA4's is a recurring job. CM360 is the ad server's view; GA4 is the site's view; they will not match exactly, and knowing which dimension scope you queried is half of explaining why.

An agent connected to both can pull them in the same run and explain the gap rather than making you export two reports and eyeball them — see CM360 reporting automation, or put the reconciliation on a self-refreshing dashboard so it's current whenever someone asks.

Frequently asked questions

What does "First user CM360 advertiser name" mean in GA4?: It's the user-scoped version of the CM360 advertiser dimension — the advertiser whose CM360 ad first brought that user to your site. The unprefixed "CM360 advertiser name" is session-scoped and reflects the ad that drove the specific session instead.
What's the difference between "First user CM360" and "CM360" dimensions?: Scope. "First user" dimensions are user-scoped and attributed to the user's first touch; the unprefixed versions are session-scoped. Both are correct — they answer different questions, and mixing them in one report is why numbers often fail to reconcile.
Why are my GA4 CM360 dimensions showing (not set)?: Most often the CM360-to-GA4 link isn't configured (or is on a different property), or Floodlight tags aren't firing. It's also legitimately (not set) for any session with no CM360 exposure — organic, direct and non-CM360 paid traffic included.
Which CM360 dimensions are available in GA4?: Advertiser, campaign, placement (including placement cost structure) and creative (name, ID, type, type ID, version, format), plus CM360 source/medium — each available in both user-scoped "First user" and session-scoped variants.
Will CM360 dimensions backfill after I set up the link?: No — they populate from when the link is active onward, so date ranges before the link was configured will show (not set).