How it works
You add the MMP's SDK to your app and connect your ad networks. When someone taps or sees an ad, the network or a tracking link records that engagement. When the app is first opened, the SDK reports the install and the MMP matches it to an earlier engagement using the signals each platform allows: the Play Install Referrer and the advertising ID on Android, the IDFA with the user's permission on iOS, claims from self-attributing networks, and Apple's SKAdNetwork postbacks. The result is sent back to the networks as postbacks and shown in reports next to cost, revenue and retention.
Why it matters for an app team
Every ad network counts conversions by its own rules, so their reports add up to more installs than you really had. An MMP credits each install once, which makes cost per install and ROAS comparable across channels. One SDK also replaces a separate SDK for every network.
In practice
Example with made-up numbers: in one week three networks report 500, 400 and 300 installs, 1,200 in total, but the app was opened for the first time on 1,000 devices. The MMP attributes 700 of those installs to the three networks, once each, and counts the remaining 300 as organic.
Common confusion
An MMP is not a product analytics tool and not an ad network. It does not buy media, and it focuses on where users came from rather than on every screen they visit. You will also see it called a mobile measurement partner or an attribution provider; the terms mean the same thing.