Fix "Unassigned" or "(not set)" traffic in GA4

1. 1In Google Analytics, open Reports, then Acquisition > Traffic acquisition. The table opens on Session default channel group; note how many sessions show as Unassigned.
2. 2Click the drop-down at the top of the table's first column (Session default channel group) and choose Session source / medium.
3. 3Read the rows that do not belong to a channel you recognize. A named source with an unusual medium, such as a listing or QR tag, is a link tag. A named source with (not set) as the medium may be a link tagged without utm_medium. A row where both source and medium read (not set) points to how the tag is set up on the site.

1. 1A link tag with a medium no rule matches. GA4 files a visit under a channel only when its source or medium fits Google's rules, for example medium exactly organic for Organic Search, referral for Referral or email for Email. A medium such as cpc, ppc or one starting with paid files the visit as Paid Other unless the source is on Google's list of search, social, video or shopping sites. Retag the link with a medium from those rules. Google's own UTM best-practice table shows organic_search as an example medium, yet the Organic Search rule needs the medium to be exactly organic or the source to be a search site, so that tag can land in Unassigned.
2. 2A link tag with no medium. Google says missing UTM parameters result in (not set) values, and recommends setting all the relevant ones, especially utm_source, utm_medium and utm_campaign. Add the missing medium to the link.
3. 3(not set) source and medium. Google says this happens when a session is missing its session_start event, which can happen when the Google tag does not fire on an Initialization trigger. In Tag Manager, open your Google tag, click Triggering, choose Initialization - All pages, remove the old trigger, save, then Submit and Publish.
4. 4(not set) on a site with a cookie banner. Google names two consent mode mistakes: using the default command where the update command belongs after the visitor answers the banner, and sending events marked denied after the visitor granted consent. Either splits a session from its start. Have whoever set up the banner check both.
5. 5(not set) that persists after both checks. Google also lists tag settings that break session identity: the Google tag firing after other events on the page, an inconsistent cookie prefix across the site, a cross-domain linker that starts late, and custom client or session IDs. Have whoever installed the tag check each one.

Tags and triggers count from the day they change. Sessions already recorded as Unassigned stay that way in the default channel group. (not set) in the Google Ads columns of Advertising reports, such as campaign or ad group, is a different problem: Google points to an unlinked Google Ads account, auto-tagging switched off, or another Google Ads account advertising the site that is not linked to this property.

1. 1Click Admin and, under Data display, click Channel groups.
2. 2Click Create new channel group. Google starts it as a copy of the default group.
3. 3Click Add new channel, name it, click Add condition group, and set a condition that matches only the tag you identified, such as Medium exactly matching the value your listing link uses. Click Save channel.
4. 4Click Reorder, drag the new channel above the channels that would otherwise catch it, click Apply, then Save group.
5. 5Use the new group as the first column in Traffic acquisition. Google applies custom channel groups to past data too.

Never add a channel that catches (not set) and calls it organic or direct. A visit with no recorded source is unknown, and labeling it organic makes a channel look stronger than it is.