Topic
What Amazon, Etsy, Walmart, and eBay actually give you — auth models, data gaps, and the integration problems that only show up once you're multi-marketplace.
5 guides, written from real builds.
Marketplace APIs
If you're integrating more than one marketplace, the authentication layer is where your abstraction breaks first. All four use OAuth 2.0 on paper, and no two behave the same way in practice. Here's what actually differs — token lifetimes, rotation, credential ownership — and how those differences should shape your database schema.
Marketplace APIs
Your carrier API rejects the shipment because the consignee phone is missing, and the order payload simply doesn't contain one. That's not a bug in your integration — Etsy and Walmart don't return a buyer phone at all, and Amazon's is a relay number. Here's what each marketplace actually gives you and how to satisfy the carrier without inventing data.
Marketplace APIs
Your Etsy integration works for weeks, then a shop quietly stops syncing and only a human re-login fixes it. That is the rotating refresh token: Etsy issues a new one on every refresh and kills the old, so a crashed write or two concurrent syncs orphan the shop. Here is the mechanism, the scheduled-vs-manual sync race, and the cache-plus-lock fix.
Marketplace APIs
You went looking for a Selling Partner API endpoint that returns the messages buyers send you, and there isn't one — Amazon's Messaging API only sends. Here's why the read side doesn't exist, and the email-relay ingestion pattern that gets buyer messages into your own app instead, matched to the right order and the right seller account.
Marketplace APIs
Marketplace syncs are almost always written as upserts, which means they can create and update rows but can never remove one. When an order disappears upstream — a receipt that starts 404ing, an order that ages out — it lives in your database forever, quietly inflating counts and revenue. Here's how to detect phantoms without deleting real data by mistake.
Shahzeb Khan runs Databaaba, a one-person studio that builds marketplace apis integrations for sellers, agencies, and software teams. Every guide here came out of a real client build.