Hi @User81578, welcome to the Sonos Community!
Are you able to use Google Assistant with other music services or do you receive the same error? What if you ask some basic commands like the time, does the system respond?
You’ll need to use BBC Sound to play Radio 2 on Sonos, and unfortunately this isn’t possible to do with Google Assistant currently, you can read more about this on BBC Sound page: Help fixing problems with BBC Sounds on your Sonos device.
It’s also possible that TalkSport is region locked and your region isn’t set correctly on Sonos. Check you’re in the correct region by going to Sonos.com → Profile → Edit Profile → Address Information → Make sure Country is correct then save changes. After you’ve done that, it can take a while for the system to change over, but a reboot of your Sonos system may speed this up.
I hope this information helps!