Finalizes and accepts a Stripe quote, creating the (open, unpaid) invoice and advancing the linked experiment to WaitingForMaterials. Optionally attach a purchase order number for your records.

A JSON body is required. Every field of ConfirmQuoteRequest is optional, so a caller with no purchase-order number and no notes sends {} — the refusal says so if they forget (BUG-0059).

This endpoint is categorically non-settling: it never settles a payment and never emits a payment 402. The 200 response carries the finalized invoice plus a HATEOAS payment pointer telling you where and how to pay — the Stripe-hosted page for an async-invoice quote, or POST /invoices/{invoice_id}/pay for a machine rail (x402-exact / mpp-spt), where the 402 challenge is answered.

The quote must be in a confirmable state ("Waiting for confirmation" or "Quote sent") and must not already have an invoice. Expired or otherwise non-confirmable quotes return 409.

{
  "notes": "Please expedite processing",
  "purchase_order_number": "PO-2026-00142"
}

{
  "hosted_invoice_url": "https://invoice.stripe.com/i/acct_1234/test_5678",
  "payment": {
    "hosted_invoice_url": "https://invoice.stripe.com/i/acct_1234/test_5678",
    "methods": [
      "x402-exact",
      "mpp-spt"
    ],
    "pay_url": "/api/v1/invoices/in_1OqLk2LkdIwHu7ix6OboRpXl/pay"
  }
}