Mobile payment integration is the process of adding payment functionality to iOS and Android apps. It includes in-app purchases (subscriptions, one-time items), digital wallets (Apple Pay, Google Pay), and payment gateway integration (Stripe, PayPal). Payments in mobile are complex because the app must communicate with app stores (Apple, Google), payment processors (Stripe), and your backend server. Data flows through multiple systems, and PCI compliance (secure card handling) is mandatory.