This information can only be entered in case of a shipment of sub-contractor type and, in this case, it is mandatory. It corresponds to the sub-contractor location that must be reordered in case of sub-contractor shortages. This location is initialized by default by the sub-contractor location defined in the ship-to customer record, then by the location defined in the supplier record if the location is not entered in the shipment address (on the condition that the location specified in the supplier exists in the shipment site). This location can however be modified from the moment the chosen location is of the sub-contractor type and belongs to the shipment site.