How it works
An MMP SDK in the app records installs and events. The MMP matches them to ad clicks and impressions it receives from ad networks, and credits the right campaign. Well-known MMPs include AppsFlyer, Adjust, Branch and Kochava.
What changed on iOS
Since App Tracking Transparency (ATT), apps need permission to use the advertising identifier for tracking. Many users decline, so iOS attribution relies largely on Apple's privacy-preserving frameworks — SKAdNetwork and AdAttributionKit — with aggregated, delayed data.
On Android, the Install Referrer and Google's Privacy Sandbox for Android play a similar role.
Why it matters
Without attribution you can't calculate cost per install or compare campaigns against lifetime value — the basis of every user acquisition budget decision.
Example
A team runs ads on three networks. Attribution shows network B has the highest CPI but users who subscribe twice as often — so they shift budget to it.