I can control Sonos from ANY wifi network, using VPN connection to my home server. All ok and it works.
And then there is a stupid limitation imposed by Sonos- I cannot do the same while I am on mobile connection. I could use VPN to appear to be in my home network where my Sonos is but I cannot because S2 app gives me an error.
I am probably one of 3 people in the world being bugged by this “feature”.