You are best advised to use your own recording equipment and not to inform the DWP that you are making a recording. In the past Benefits claimants have submitted the form to the DWP requesting that the interview be recorded but then on the day they are told that the equipment has faulted or that their request hasn't been processed yet. As for recommendations about Apps or equipment you would be best advised by other Forum members.
Hope this helps David
Nothing on this board constitutes legal advice - always consult a professional about specific problems