Testing an AI shopping agent's checkout flow? There's no sandbox for that yet — so I built one

If you're building or evaluating an AI agent that can shop and check out on its own, you've probably run into the new "agentic commerce" protocols: ACP (OpenAI + Stripe + Meta), AP2 (Google), and UCP. They define how an agent talks to a merchant to create a checkout session, apply a payment token, and get an order back. Stripe's own test mode covers the payment half fine — test cards, test API keys. But there's no hosted "fake merchant" you can point your agent at to verify the protocol half: does your agent correctly create a session, handle a 422 idempotency conflict, parse the order response, retry politely? You either mock it yourself from the spec, or risk finding out against a real merchant. So I built acp-sandbox — a small hosted mock merchant implementing the ACP checkout API, live at https://acp-sandbox.flo-voice1.com . What it does It implements the real checkout_sessions lifecycle from ACP's 2026-04-17 spec : create, retrieve, update, complete, cancel. Responses match the actual CheckoutSession / Order / Error schemas for the fields it supports — I pulled the OpenAPI spec directly rather than guessing field names. # get a test key, no signup curl -X POST https://acp-sandbox.flo-voice1.com/keys \ -H "Content-Type: application/json" -d '{"email":"you@example.com"}' # create a session against the demo catalog curl -X POST https://acp-sandbox.flo-voice1.com/checkout_sessions \ -H "Authorization: Bearer acps_test_..." \ -H "Content-Type: application/json" \ -d '{"line_items":[{"id":"item_demo_headphones","quantity":1}],"currency":"usd"}' Every request/response is logged per API key ( GET /logs ), so you can see exactly what your agent sent when something doesn't work. What it deliberately doesn't do (yet) No real payment processing — complete always succeeds once you send any payment_data . No OAuth delegate_authentication flow. No fulfillment options (shipping/pickup) — every session goes straight to ready_for_payment . Fixed demo catalog (4 items), not a rea