Applies to: All Reolink devices which can support audio function 

You could follow the articles below to enable audio for recording and live viewing:

How to enable audio for recording and live viewing on Reolink app

How to Enable Audio for Recording and Live Viewing on Reolink Client

How to enable audio for recording and live viewing on WiFi NVR

How to enable audio for recording and live viewing on POE NVR

How to enable audio for recording and live viewing on Web Browser