TL;DR: I built a platform syncing 50k+ SKUs across 5 Amazon marketplaces. Polling the Catalog API nearly killed it. Switching to event-driven inventory sync (Notifications API → SQS → Lambda) cut sync latency from 24 hours to under 15 minutes and dropped API call volume by 90%. Here's everything I wish I'd known going in.
Amazon's Selling Partner API is powerful and genuinely complex. The official docs are long and the gotchas are buried. After building a production platform managing 50,000+ SKUs across 5 marketplaces, this is my ground-level guide — auth, rate limits, sync architecture, and a repricing engine that holds up under real load.
The auth story nobody explains clearly
SP-API does not use IAM credentials the way most AWS services do. The flow is:
Register your app in Seller Central and get an LWA (Login with Amazon) client ID and client secret.
