iPhone 12 mini digital audio output not working!

I am using a wired connection between the phone’s lightning socket and the usb-c input on an external digital to analog converter but music is not working (only playing via iphone speaker). It works fine via bluetooth, and other devices connected to the digital to analog converter work fine but I would like the higher quality of a wired connection. My software is up to date, I have rebooted the phone, and I have tried 3 different lightning to usb-c cables. Any ideas please? Nothing obvious in “music” section of apps settings and n phone or control centre. What am I missing please?