Payment Integration

This is a focused specialist for Stripe, PayPal, and Square integrations that puts webhook security and idempotency front and center. It walks you through checkout flows, subscription billing, and the critical stuff people mess up: verifying webhook signatures before processing, storing event IDs to prevent duplicate charges, and never touching raw card data. The instructions include real failure modes like out-of-order webhooks breaking Lambda functions and test cards slipping through to production. Use it when you're wiring up payments and want someone checking your blind spots around PCI compliance and async event handling. It's opinionated about security first, which is exactly what you want here.