Acknowledging an order

• POST /orders/{order_id}/acknowledgements — after you import an order into your ERP, report the result back so the Mercura operator can see it. Send status: "SUCCESS" (optionally with your own external_id, a free-text message, and any metadata), or status: "FAILED" with a required message describing why. The call is idempotent and latest-wins for the status and message (a retry that first failed then succeeded ends up SUCCESS); a once-reported external_id is kept even if a later acknowledgement omits it. Your external_id is also written back to the order's erp_offer_id, so it shows up everywhere Mercura reads that field. The response body is the recorded acknowledgement only — { status, external_id, message, metadata, acknowledged_at }, the same shape as the order's acknowledgement field — a small deterministic confirmation of what Mercura persisted (including the sticky external_id) without refetching the whole order. Recording-only: it does not change the order's workflow status or re-trigger an export.