Most ‘guest’ networks are set up to allow the user (device) to connect to the internet, but not any other devices that are on that same ‘network’, such as any Sonos devices, or a controller device. 

How certain are you that this network is defined as a ‘guest’ network? Is there any possibility to connect to the ‘standard’ network, with both the Sonos and your controller device?

Frequently, in situations of a similar type, a travel router can be useful, it allows you to connect to the third party network, and create your owned controlled network for your Sonos and controller so that they’ll communicate properly with each other. 

LOL, this is a UX fiasco 

Sonos products are being sold as a BLUETOOTH SPEAKERS… only after you buy it you suddenly find out that in order to use bluetooth you HAVE TO CONNECT YOUR SONOS TO WI-FI! How on earth is that even related???

And in case you live in a hotel with a passwordless wi-fi network (name + room number instead) - congrats, you’ve just bought a useless piece of junk 

Never again.