I have just got a Pirate-Audio hat on my Pi and Mopidy is working great.
When I was setting it up, I used the server light version of raspberry pi os not the desktop.
As a result I suspect that I am missing audio software (Alsa or Pulse??) to control volume. The volume buttons on the Pirate-Audio hat are not having any effect . Same with volume controls on mobile app. However the volume control in musicbox webclient works!
Any suggestions as to how I could fault find that problem??
Problem solved. It was a case of adding