iOS In-App Subscription Tutorial with StoreKit 2 and Swift

This tutorial provides a comprehensive guide to implementing in-app purchases using Apple's StoreKit 2 framework across iOS, macOS, watchOS, and tvOS apps, accompanied by code examples and a sample app. It outlines the setup of App Store Connect and StoreKit configuration files, detailing the process from listing and purchasing products to unlocking in-app features and handling transactions offline. The tutorial emphasizes the use of Swift for implementing on-device subscriptions and explores the benefits and limitations of using a server backend for subscription management, including the advantages of real-time notifications and comprehensive subscription management offered by server-side integration. Additionally, it addresses the use of App Store Server APIs and notifications for monitoring purchases and provides insights into the design and benefits of a server-based approach, while also highlighting the role of services like RevenueCat in simplifying the integration and management of in-app purchases.