6.3.2.5 Update UI with status of machine engine

While connected to a machine engine, the UI needs to check the status of the machine engine, by subscribing to the corresponding Variables of the Status Object of the machine engine.

In addition, it needs to subscribe to the DeliveryRequests and DeliveryProgress Variables of the Delivery Object of the machine engine. This may be done when connecting to the machine engine and is required once the UI has started a deliver request via the payment service using the DeliverRequest Method of the Delivery Object of the payment service.