Array of easyship_shipment_id values (e.g. ESSG10006001) — Easyship's unique shipment identifier, prefixed with ES and the destination country code, as returned by the Shipment API. Required for couriers that need explicit shipment selection. Any IDs that do not belong to your account are silently dropped — the manifest will be created with only the matched shipments and no error is returned. (see Supported Couriers and Conditions for details).