Payment Integration Overview This skill covers implementing payment processing and subscription billing in web and mobile applications. It addresses Stripe integration (Checkout, Elements, PaymentIntents), subscription lifecycle management, webhook handling with idempotency, PCI compliance, metered and usage-based billing, tax calculation, refund processing, and RevenueCat for mobile subscriptions. Use this skill when adding payment processing, building subscription billing, handling Stripe webhooks, implementing pricing pages, managing payment failures, or integrating mobile in-app purchases…