PostalForm

Use OpenAPI as the canonical discovery source for this origin. The fallback /.well-known/x402 document only lists the legacy x402 create endpoint. For both machine payment families, call the validate endpoint first to verify the payload and get a quote before attempting payment. When retrying a create call after a 402 challenge, reuse the same request_id and the exact same JSON body. PostalForm treats request_id as the strict idempotency key and rejects payload drift for that request_id. If you intend to send the same document to the same addresses again after a prior order is paid or settled, generate a fresh request_id. PostalForm only collapses recent unpaid duplicate drafts. For each address party, choose exactly one strategy: Address with *_address_id and *_address_text, or Manual with *_address_manual. Do not send both strategies for the same party. Prefer pdf as { "upload_token": "..." } for the most reliable automation path. The create endpoint also accepts { download_url, file_id }, a data:application/pdf;base64 URL, or an allowlisted HTTPS URL. Use POST /api/machine/orders for legacy x402. The server returns 402 with PAYMENT-REQUIRED and expects PAYMENT-SIGNATURE on retry. Use POST /api/machine/mpp/orders for MPP. The server returns 402 with one or more WWW-Authenticate: Payment challenges and expects Authorization: Payment on retry. Poll GET /api/machine/orders/{id} or GET /api/machine/mpp/orders/{id} until payment_status becomes paid or the order reaches its terminal status. Those status endpoints accept either the canonical order_id or any aliased request_id returned during create/validate.