Refused (409 state_conflict) when shipments or captured payments exist, or a purchase order was accepted into it: cancel it instead. Otherwise one unit removes its fulfillment orders (open reservations released), its invoices and payments, then the order; nothing is orphaned. Answers the order as it was.

Scope: orders:write, channel:write or admin. A permission group made before the Channel API scopes existed grants it as orders:manage.

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.