universal-checkoutlisted

# Universal Checkout Discover, buy, track, and return products across US online retailers through the Zinc API (`https://api.zinc.com`). One API covers Amazon, Walmart, Target, Best Buy, eBay, Home Depot, Lowe's, Wayfair, and 50+ more. > Live supported-retailer list: `GET https://api.zinc.com/retailers` (free, no auth). If an agent only ever buys from one store, there are also per-retailer skills (`amazon-checkout`, `walmart-checkout`, …) — see the repo README. ## Quick Start **Which auth method should I use?** - **`ZINC_API_KEY` env var is set** → Use `POST /orders` with Bearer token auth. This is the standard flow for pre-registered users. - **MPP — no account needed** → Use the `/agent/*` endpoints and pay per request with a **Stripe card** (via Stripe Link — no crypto), **Tempo** stablecoins, or **x402** (USDC on Base). `POST /agent/orders` to buy; `/agent/search` to discover ($0.01 per data call). `GET /retailers` is free. - **Neither is set** → Ask the user to either sign up at [app.zinc.com](https://app.zinc.com) for an API key, or set up an MPP payment method. Try it without code at [agent.zinc.com](https://agent.zinc.com). All amounts are in **US cents** (e.g. `5000` = $50.00). ## Authentication ### API Key Auth ``` Authorization: Bearer $ZINC_API_KEY ``` ### MPP Auth (Machine Payments Protocol) MPP is an open standard for HTTP 402 machine-to-machine payments (spec: [mpp.dev](https://mpp.dev)) — no API key needed upfront: 1. Send the request (e.g. `POST /