Payment Gateway Integration

This handles the standard payment gateway integrations you need for e-commerce: Stripe, PayPal, and Square. It covers payment intents, subscription billing, webhook verification, and refund handling across Python/Flask and Node.js/Express backends. The reference guides include actual working code for creating payment intents, managing subscriptions, and properly verifying webhook signatures. Best practices emphasize the obvious security stuff like never storing raw card data and always verifying webhooks, but also practical details like using idempotency keys and testing in sandbox mode first. If you're building anything that takes money online, this gives you the boilerplate to start processing payments without making the common security mistakes.