A beginner running a small course-selling site saw something absurd in the acquisition report: their #2 referral source was their own payment processor's domain.
The clue: every purchase routed through a hosted checkout, then bounced the buyer back to the thank-you page. GA4 read that return as a brand-new session from a new source. The original Google or Facebook session got the credit stolen mid-funnel.
The change was one line in admin: add the processor domain to the unwanted-referrals list, so returns stay attributed to the real source.
The result: paid-search conversions in the report jumped from 31 to 73 in a month, no extra spend. The sales were always there; the credit was leaking to checkout.com.
The knock-on: they'd nearly paused Google Ads for "underperforming." The fixed report showed it driving most revenue.
Lesson: a payment domain in your top referrals isn't traffic. It's your attribution leaking out the back door.
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"Why is my own checkout my top traffic source?"
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