Payment Gateway Integration

Covers the essentials for integrating Stripe, PayPal, or Square into your app with working code for payment intents, subscriptions, refunds, and webhook verification. The examples are Node.js focused and include the nitty-gritty details like converting to cents, handling signature verification, and expanding invoice objects. The security checklist is actually useful (verify signatures, use idempotency keys, never log card numbers). What's good here is it doesn't try to abstract away the payment provider, it just shows you the practical patterns for each one. You'll still need to read the official docs for your specific use case, but this gets you past the initial setup hurdles and reminds you about the compliance stuff you might forget.