paypal-integration

# PayPal Integration Master PayPal payment integration including Express Checkout, IPN handling, recurring billing, and refund workflows. ## Do not use this skill when - The task is unrelated to paypal integration - You need a different domain or tool outside this scope ## Instructions - Clarify goals, constraints, and required inputs. - Apply relevant best practices and validate outcomes. - Provide actionable steps and verification. - If detailed examples are required, open `resources/implementation-playbook.md`. ## Use this skill when - Integrating PayPal as a payment option - Implementing express checkout flows - Setting up recurring billing with PayPal - Processing refunds and payment disputes - Handling PayPal webhooks (IPN) - Supporting international payments - Implementing PayPal subscriptions ## Core Concepts ### 1. Payment Products **PayPal Checkout** - One-time payments - Express checkout experience - Guest and PayPal account payments **PayPal Subscriptions** - Recurring billing - Subscription plans - Automatic renewals **PayPal Payouts** - Send money to multiple recipients - Marketplace and platform payments ### 2. Integration Methods **Client-Side (JavaScript SDK)** - Smart Payment Buttons - Hosted payment flow - Minimal backend code **Server-Side (REST API)** - Full control over payment flow - Custom checkout UI - Advanced features ### 3. IPN (Instant Payment Notification) - Webhook-like payment notifications - Asynchronous payment updates - Verific...