Ring Intercom Videx 3011

I have just purchased and installed the Ring Intercom to my Videx 3011 intercom. Instructions all very easy to follow, and wired correctly as per the app - double checked with technical support.

I can open the door through the app, and when the door is rung I am instantly informed via the app. People at the door can hear me talking very clearly from my ring app, but I cannot hear them.

If someone shouts into the microphone hole on the videx unit at the front door, you can JUST about hear a muffled voice… The videx unit telephone still works perfectly with crystal clear audio.

I’ve contacted RING techincal support who are looking into it, but I wondered if anyone had any experience of a similar issue, and what the fix was?