"We tag TikTok Ads with utm_source=tiktok-ads. It's clearly an ad, right?"

If that's been your team's convention, GA4 has been silently dropping your TikTok paid clicks into (other) for as long as that tag has been in production. This isn't a misconfiguration or a GA4 bug — it's the result of GA4's officially distributed source list containing exactly 5 rows for TikTok and LinkedIn combined, and tiktok-ads not being one of them.

This post walks through what to put into utm_source for TikTok Ads and LinkedIn Ads, working from the 5 official rows GA4 actually evaluates.

TL;DR

• Use utm_source=tiktok or utm_source=linkedin — the lowercase shortform is the shortest exact match on GA4's official source list
• Never use tiktok-ads, linkedin-ads, tiktok_ads, linkedin_ads — none of them are registered, all of them drop into (other)
• Shortlinks and mobile subdomains are not registered either — vt.tiktok.com / m.tiktok.com / m.linkedin.com fail SOCIAL judgment (only LinkedIn's lnkd.in is registered)

1. How GA4 decides "Paid Social"

GA4's Default Channel Group auto-classifies each hit by utm_source × utm_medium. A session lands in Paid Social when both conditions hold:

• utm_source matches a value registered in GA4's "social sites regex list"
• utm_medium matches ^(.*cp.*|ppc|retargeting|paid.*)$

The "social sites regex list" itself is distributed by Google as an .xlsx file (delivered as PDF) with 819 entries of source names paired with category labels. Whether TikTok or LinkedIn gets Paid Social judgment depends not on industry convention or tool defaults — it depends on this single file.

The utm_medium side is fully unpacked in the sister post on Meta Ads utm_medium. This one focuses on utm_source, reading the TikTok and LinkedIn rows.

2. The 5 official rows

Out of the 819 entries on the official list, the rows for TikTok and LinkedIn are exactly 5. Three facts stand out from those 5 rows:

1. All 5 rows are SOURCE_CATEGORY_SOCIAL — the Source-side condition for Paid Social is met only on an exact match of one of these 5 strings
2. TikTok has 2 rows, LinkedIn has 3 — only LinkedIn includes its official shortlink lnkd.in, which makes mobile referrals easier to capture
3. No variants at all — tiktok-ads / tiktok_ads / TikTok-Ads / linkedin-ads / linkedin_ads / m.tiktok.com / vt.tiktok.com / m.linkedin.com all fail to match any row

The name "social sites list" suggests every TikTok or LinkedIn variant is covered. In reality, only one lowercase shortform plus one or two domain forms are present. Because Google may update the file at any time, when you use this in production work, download a fresh copy each time rather than caching values from a blog post.

3. Four failure modes for utm_source

Failure 1 — tiktok-ads / linkedin-ads disappear from Paid Social. Media name + -ads reads naturally to internal operators, but neither value is registered. Sessions show up as tiktok-ads / cpc on a standalone row and never enter the Paid Social aggregate. Monthly reports look like "Paid Social revenue dropped" when classification just detached.

Failure 2 — TikTok / LinkedIn (mixed case) splits one campaign into two rows. GA4 stores utm_source case-sensitively. With tiktok and TikTok coexisting in the same campaign, the report shows two rows. Only the lowercase side passes Paid Social judgment; the mixed-case side falls into Referral or (other).

Failure 3 — vt.tiktok.com / m.tiktok.com / m.linkedin.com (shortlinks and mobile subdomains) are not judged as SOCIAL. TikTok's in-app share generates vt.tiktok.com referrals, TikTok mobile sends m.tiktok.com as the host, LinkedIn mobile arrives via m.linkedin.com. None of these match any of the 5 rows. Even non-ad organic traffic stacks into Referral / (other). Only LinkedIn's lnkd.in is registered, so internal shares via that shortlink do get SOCIAL recognition.

Failure 4 — tiktok_ads / linkedin_ads (underscores) also disappear. Same as the hyphen-separated form. utm_source matching is exact-string only, unlike utm_medium regex, so any near-miss falls into (other) immediately.

4. Recommended format

# TikTok Ads
utm_source=tiktok
utm_medium=cpc
utm_campaign={{campaign.name}}
utm_content={{ad.name}}
utm_id={{campaign.id}}

# LinkedIn Ads
utm_source=linkedin
utm_medium=cpc
utm_campaign={{campaign.name}}
utm_content={{ad.name}}
utm_id={{campaign.id}}

Three reasons to recommend tiktok / linkedin:

• Shortest exact match on the 5-row list — near-zero typo risk
• Reads cleanly across the org — the media name itself
• Parallel to other media — facebook for Meta Ads, google for Google Ads. Cross-channel reports line up

Verification takes 2 minutes:

1. Pre-launch: TikTok Ads Manager / LinkedIn Campaign Manager → URL parameter field → URL preview → confirm utm_source=tiktok (or linkedin) is in the expanded URL
2. Post-launch: GA4 → Realtime → Source/Medium within 30 min → confirm tiktok / cpc (or linkedin / cpc) is showing

If you see tiktok-ads / cpc or (direct) / (none), the parameter never reached GA4 with a list-compliant value.

Conclusion

Across operator blogs and Twitter threads, you'll find factions arguing "for TikTok Ads, tiktok-ads is the cleanest naming" or "for LinkedIn, linkedin_ads". What GA4 actually evaluates during Paid Social judgment is TikTok 2 rows + LinkedIn 3 rows = 5 rows on the official list. tiktok-ads and linkedin-ads are not in those 5 rows. tiktok and linkedin are. That's the only fact that matters.

The long-form English write-up on RevenueScope walks through the official GA4 file download link, the 4 failure modes in more depth, and the recommended URL template with verification steps.

What's your team's utm_source convention for TikTok Ads or LinkedIn Ads? Have you hit the case-sensitivity split (tiktok vs TikTok) in the wild, or seen mobile referrals slip into (other) instead of Paid Social?