webapp-paywall-implementation

Implement paywalls, subscription billing, and feature gating in web applications. Covers Stripe/Lemon Squeezy/Paddle integration, subscription lifecycle management, React/Next.js gating patterns, webhook handling, and pricing page design. Activate on 'paywall', 'subscription', 'billing', 'Stripe integration', 'feature gating', 'pricing tier', 'payment', 'monetize', 'charge users', 'Stripe Checkout', 'webhook handler', 'subscription state'. NOT for pricing strategy decisions (use indie-monetization-strategist), not for payment UI design only (use web-design-expert), not for in-app mobile purchases (App Store/Play Store rules are a different beast).