iOS 18 and the slow death of last-click attribution

Every iOS release since App Tracking Transparency has chipped away at what ad platforms can directly observe. Last-click attribution, which was already a simplification, is now closer to a guess dressed up in a dashboard, and most advertisers haven't updated how they read it.

The practical symptom is a platform reporting strong ROAS while contribution margin quietly declines. Both can be true at once: the platform is crediting itself for conversions it merely touched, while genuinely new customer acquisition slows.

The fix isn't a single tool, it's a discipline: server-side event tracking to recover signal loss, incrementality testing (geo holdouts or platform-off tests) run quarterly rather than assumed, and a media mix model, even a simple one, that doesn't depend entirely on any single platform's self-reported numbers.

None of this makes attribution perfect; nothing will again. But it moves the scaling decision from "trust the dashboard" to "trust the P&L," which is the only version of trust that survives the next iOS update.