Spotify Connect: how to config UFW firewall on remote system

So I have Volumio x86 installed on a little netbook and working fine, web access works flawlessly. I have installed the Volumio Spotify Connect2 plugin. When I start Spotify on my Ubuntu 16 laptop (either desktop app or the web player), the volumio device does not show up in my list of Spotify Connect devices. However, on my girl friend’s laptop (running Windows 10 with Eset Internet Security firewall) the volumio device is visible and thus can be selected.

When I completely disable the UFW firewall on my ubuntu laptop, the volumio device shuddenly shows up. So this is obviously a firewall issue. The question then: which port(s) do I have to open on my ubuntu laptop for Spotify Connect to work?

Note: I have no problem connection to other Spotify sessions with UFW enable on other devices be they running ubuntu, Windows or Android.

Greetings, Spotify Connect (with volspotconnect2) has two modes - discovery (that uses mdns) and regular mode where you login using your credentials. For the discovery (aka multi-user on the plugin settings page) the receiver broadcasts the service type _spotify-connect._tcp. So check your firewall logs if its blocking said service, and then you will have to figure out what settings you need to enable in your firewall to allow these multicast/mdns packets through.