Optional. Submit Supplier order ID before driver assigned. Per agreement, shall be called by a supplier for on-demand rides only. Right after order request is received from Gett and order is successfully created on supplier system side. The API is to be used to report Gett an external_order_id (order ID from a supplier system) before Accept Order call, so Gett will have a reference number that can be used if needed for manual operations, such as support channels, financial flows or reporting.