Every line must name a product (422 unresolved_reference otherwise). The order is created through the orders create unit (lines, totals, tagging rules), then the purchase order is marked accepted with its sales order, and the 855 acknowledgment follows through the po-accepted message. outcome updated the first time, unchanged after.

Scope: purchase-orders:write, channel:write or admin.

Idempotency: send Idempotency-Key; a retry with the same key replays the first answer.

Rate limit: write class, 1,200 requests per minute per tenant by default (read class 6,000). Every response carries X-RateLimit-Limit, X-RateLimit-Remaining and X-RateLimit-Reset; a refusal is 429 rate_limited with Retry-After.