Starting flatpak under cage?

Hi I’m using cage as DE on my HTPC, and want to start the flatpak rocks.shy.VacuumTube. Now this is the first time I’m using flatpak so I might be doing things wrong. I have the following config for cage and audio: users = { users = { htpc = { uid = variables.users.htpc.id; isNormalUser = true; extraGroups = [ # allow htcp access to keyboards "input" "dialout" "video" "render" "audio" ]; ...