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All eighteen Firebase services from Expo and React Native — the two-SDK fork that silently breaks half the tutorials online, modular TypeScript for every product, the full module matrix, what each one bills on, and the RN-specific traps. Ends with a worked example.

How in-app ads work end to end — the marketplace, the life of an ad request, bidding vs waterfall, Meta Audience Network through AdMob mediation, Kotlin on the Next-Gen SDK, consent, policy, payouts and the setup mistakes that stop ads serving.