Universal Checkout

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 for an API key, or set up an MPP payment method. Try it without code at 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) — no API key needed upfront:

1. Send the request (e.g. POST /agent/orders) with no Authorization header → HTTP 402 Payment Required. The challenge advertises every available rail: MPP methods as one WWW-Authenticate: Payment … header each (method="stripe", method="tempo"), and x402 as a PAYMENT-REQUIRED header (USDC on Base).
2. Pick the rail your client supports and pay, then retry: MPP methods resubmit with Authorization: Payment <credential>; x402 clients resubmit with a PAYMENT-SIGNATURE header. Client libraries handle this loop automatically.
3. For orders, save the X-Api-Key response header — a Bearer token scoped to that order, for GET /orders/{id}.

Select a single rail with ?method=. A 402 can carry several challenges at once, and many HTTP clients mishandle repeated WWW-Authenticate headers (they fold them into one comma-joined value, corrupting the params). If your client only supports one rail, append ?method=stripe, ?method=tempo, or ?method=x402 to /agent/orders to get a single, unambiguous challenge. Omit it to advertise all rails (for discovery). If you do parse multiple challenges yourself, read the raw header list (in Python httpx, resp.headers.raw) and select by method=.

Payment methods:

Find a product (optional)

If the user gives you a product URL, skip to Place an order. Otherwise find an orderable product first:

curl "https://api.zinc.com/search?q=cast+iron+skillet" \
  -H "Authorization: Bearer $ZINC_API_KEY"

GET /search returns { status, query, results: [...] } across retailers; each result has a directly orderable url plus retailer, title, price (cents), stars, available. Pass a result's url straight into an order.

Paying via MPP (no account)? Use the metered POST /agent/search instead — $0.01 per call, returns a Payment-Receipt header; the MPP client handles the 402 → pay → retry automatically. GET /retailers is free.

Richer product data (Amazon & Walmart only). For best-price comparison on those two, use GET /products/search?query=<term>&retailer=amazon|walmart (returns product_id, price, ship_price, stars, …) and GET /products/{product_id}/offers?retailer=amazon|walmart to compare offers by price and condition before ordering. On the MPP rail these are POST /agent/products/search, POST /agent/products/offers, and POST /agent/products/details, $0.01 per call.

Place an order — POST /orders (or POST /agent/orders for MPP)

Required fields:

• products — array of product objects (see below)
• shipping_address — US delivery address
• max_price — integer, the maximum total in cents Zinc may spend before finalizing (your price ceiling)

Product object:

Condition enum: New, Refurbished, UsedLikeNew, UsedVeryGood, UsedGood, UsedAcceptable.

Shipping address: first_name, last_name, address_line1, address_line2 (optional), city, state (2-letter), postal_code, phone_number, country (defaults to US).

Optional order fields: handling_days_max (integer ≥1 — cap on seller handling time, the lever for bounding how fast it ships), is_gift (boolean — suppress prices on the packing slip), idempotency_key (string ≤36 chars), metadata (object), po_number (string).

Controlling price & shipping

There is no shipping-method picker; control cost and speed with: max_price (price ceiling), condition_in (allow used/refurbished for a cheaper qualifying offer), and handling_days_max (cap handling time). max_price is the total ceiling — item + shipping + tax — so leave room for shipping (see GET /retailers for each retailer's free-shipping terms).

Order statuses: pending → in_progress → order_placed | order_failed | cancelled | cancelled_by_retailer.

Example (API key):

curl -X POST https://api.zinc.com/orders \
  -H "Authorization: Bearer $ZINC_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "products": [{ "url": "https://www.amazon.com/dp/B09V3KXJPB", "quantity": 1, "condition_in": ["New"] }],
    "max_price": 5000,
    "handling_days_max": 5,
    "shipping_address": {
      "first_name": "Jane",
      "last_name": "Doe",
      "address_line1": "123 Main St",
      "city": "San Francisco",
      "state": "CA",
      "postal_code": "94105",
      "phone_number": "5551234567",
      "country": "US"
    }
  }'

Paying via MPP — POST /agent/orders

Same request body, no API key — pay inline. Agent authorizes max_price + $1.00 upfront (the $1 is the Zinc API fee, so the full max_price stays available to the retailer). Validation runs before payment: an invalid URL/retailer/address returns HTTP 400 with no charge, and the credential stays reusable. On success: charged actual_total + $1, with any difference under max_price auto-refunded; on failure: full refund (server-side). The HTTP 201 response includes X-Api-Key (a zn_live_... Bearer token, scoped to this order) and Payment-Receipt.

• Stripe card (recommended for a human with just a card): use the create-payment-credential skill to mint a Shared Payment Token, then have that skill pay https://api.zinc.com/agent/orders?method=stripe.
• Tempo (stablecoin): npx mppx https://api.zinc.com/agent/orders --method POST --body '…', or pympp/mppx in code — the client handles the 402 → pay → retry.
• x402 (USDC on Base): any x402 client (e.g. AgentCash) pays POST /agent/orders directly off the PAYMENT-REQUIRED header.

# Tempo example — pip install pympp
from mpp.client import Client
from mpp.methods.tempo import tempo, TempoAccount, ChargeIntent, CHAIN_ID

account = TempoAccount.from_key("0x<your-private-key>")
method = tempo(chain_id=CHAIN_ID, account=account, intents={"charge": ChargeIntent()})

async with Client(methods=[method]) as client:
    response = await client.post(
        "https://api.zinc.com/agent/orders?method=tempo",
        json={
            "products": [{"url": "https://www.amazon.com/dp/B09V3KXJPB", "quantity": 1}],
            "max_price": 5000,
            "shipping_address": {
                "first_name": "Jane", "last_name": "Doe",
                "address_line1": "123 Main St", "city": "San Francisco",
                "state": "CA", "postal_code": "94105",
                "phone_number": "5551234567", "country": "US",
            },
        },
    )
    # Client handles the 402 → pay → retry flow automatically
    order = response.json()
    api_key = response.headers["X-Api-Key"]  # use for GET /orders/{id}

Track & manage orders

Get order — GET /orders/{id}

Retrieve a single order by UUID (Bearer token: ZINC_API_KEY or the MPP X-Api-Key). The response includes status, items, shipping_address, plus:

• tracking_numbers — array of { id, carrier, tracking_number, status, checkpoints, created_at }. status (always present) is the carrier-derived shipment state: pending | in_transit | delivered. checkpoints is the per-scan timeline (most recent first). Added automatically; there is no separate tracking endpoint.
• job_result (once terminal) — success, error, error_type, estimated_delivery, merchant_order_ids, and price_components (subtotal, tax, shipping, total, currency).

curl https://api.zinc.com/orders/<order_id> \
  -H "Authorization: Bearer $ZINC_API_KEY"

List orders — GET /orders

Returns { orders: [...] }. Requires Bearer token auth. Add ?include=tracking_events to also get the full checkpoints timeline.

Cancel order — POST /orders/{id}/cancel

Cancels an order only while pending (still queued); once in_progress or done it can't be cancelled. Returns 204 No Content on success.

Returns — POST /returns

Open a return against a placed order (Bearer token auth).

Response (201): { id, order_id, status, reason, items, label_urls, merchant_return_id, ... }. Return status: open → approved | denied | credited. Ship via the URLs in label_urls. Also GET /returns and GET /returns/{id}.

curl -X POST https://api.zinc.com/returns \
  -H "Authorization: Bearer $ZINC_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "order_id": "8c2d...",
    "items": [{ "order_item_id": "a1b2...", "quantity": 1 }],
    "reason": "damaged",
    "notes": "Arrived with a crushed corner."
  }'

Error Handling

See references/errors.md for the full error code reference.

Key points:

• HTTP errors return { error: { code, message, details } }
• Order processing failures appear in the order's job_result.error_type field
• Common issues: max_price_exceeded, product_out_of_stock, invalid_shipping_address
• MPP payment failures return HTTP 402 with { error: { code: "payment_failed", details: { reason: "..." } } }
• HTTP 402 without payment_failed code means the server is issuing a payment challenge (normal MPP flow — the client handles this automatically)

Order Status Tracking

Orders process asynchronously and typically take 5–10 minutes. After placing an order:

1. Wait ~7 minutes, then poll GET /orders/{id}.
2. If still pending or in_progress, poll again in 3–5 minutes.
3. Stop polling when the status is terminal.

Terminal statuses: order_placed, order_failed, cancelled, cancelled_by_retailer Non-terminal: pending, in_progress

If your platform supports scheduled tasks or cron jobs, schedule a check ~7 minutes after order creation rather than polling in a loop.

Safety

• Always confirm with the user before placing an order (POST /orders or POST /agent/orders) or opening a return. Orders spend real money.
• Reading operations (search, GET /orders, GET /orders/{id}, GET /returns) are always safe.
• Set max_price to cover the full cost — item price + tax + shipping/handling — not just the item. It's the total ceiling Zinc won't exceed, so too-low a value trips max_price_exceeded.
• MPP orders authorize max_price + $1 on the agent's payment method (Stripe card, Tempo wallet, or x402/USDC) — ensure sufficient balance/credit before placing.

Support

• Email: support@zinc.com
• Book a call with our CEO: https://cal.com/zinc-ian/15min
• Discord: https://discord.gg/cuXgfczYfj