Ring Elite can't select Digital Chime

I have a Digital door chime heath zenith tr-0070-bx. It randomly chimes for a short time when no one is at the door or has pressed the button. In the app, Mechanical Door Chime is selected. It is not possible for me to change the selection to digital. I tried deleting the Ring Elite completely and starting the installation again from scratch (of course carefully selecting Digital Door Chime on the way through). Alas when I view the settings in the app again, it still says mechanical and tapping that setting still does nothing - no options open to change to digital. (I'm using PoE and in case this is relevant, in Device Health the Ring Elite always shows as red Offline - but all the functions work great, streams video, chnage settings etc - just like you'd expect with an ethernet connection!)