Engineering. Unifying iOS and Android In-App Purchases with Kotlin Multiplatform

Kotlin Multiplatform adoption typically follows a predictable pattern: teams first extract networking, data models, and business logic into shared code, then tackle the most complex layer last: in-app purchases. The billing infrastructure represents a fundamental architectural challenge because Android and iOS billing systems share almost nothing at the implementation level. Android relies on Google's BillingClient with a PurchasesUpdatedListener pattern, while iOS uses StoreKit with transaction listeners and manual receipt verification, each backed by distinct server-side validation flows that must ultimately agree on subscription state.

For mobile studios pursuing cross-platform monetization strategies, this migration offers significant long-term benefits despite its complexity. Consolidating billing logic into a shared layer reduces maintenance burden, ensures consistent subscription handling across platforms, and simplifies future updates to payment flows. The engineering effort required is substantial because developers must bridge two fundamentally different paradigms, but the payoff in code reuse and consistency makes it worthwhile for teams committed to Kotlin Multiplatform as their primary development strategy.