If your affiliate tracking depends on a third-party script or a third-party cookie, some proportion of your referrals are not being credited — and the affiliates losing out have no way to prove it.
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What changed
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Browsers began partitioning or blocking third-party cookies by default, and content blockers went mainstream. Neither was aimed at affiliate programmes, but both catch them: to a blocker, an attribution script from another domain looks exactly like a tracker, because technically it is one.
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What first-party means here
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The click lands on your domain. The visit is written to your database. The cookie is set by your site, for your site. There is no other origin involved, so there is nothing for a blocker to block and nothing for a browser to partition.
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The part people miss
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First-party tracking is not only more reliable — it is more honest with affiliates. When attribution silently fails, the affiliate assumes their traffic did not convert. They stop sending it. You never find out why.
