Unitis need to be running firmware version 3.0 or later in order to work with the latest version 4.9, which includes the iRadio update. Unfortunately a device on an earlier firmware is incompatible.
To check the current firmware version on your device, look at the streamer settings menu in the Naim app.
Your streamer looks like it’s an older version which is not 24/192 compatible. Unfortunately the hardware is not capable of running the new iRadio service.