Unable to use the Ring app to answer door rings

We have a Ring video doorbell, having replaced a battery one to try and fix this issue. In short, either on cellular or wifi data, neither my wife or I can ever speak to anyone when they ring the doorbell. Live view works fine. We have gigabit fibre internet and 5GHz mesh wifi. I suspect this is a port / protocol issue getting blocked by my firewall, but currently can't find what I need to permit. The Ring app 'rings' on the phone, we can swipe to answer, but never get a connection either video or audio. Both phones are iPhone running iOS 17+ Any suggestion would be gratefully received.