I would try uninstalling the Spotify app from your device, and then reboot the device. Finally, reinstall the Spotify app, which should force a new ‘handshake’ between the two apps. 

It’s somewhat harder for Sonos folks to help here, since they don’t have visibility into the Spotify app’s code base or any logs it may generate, they’d only be able to look at the Sonos logs, which would show, as you say, that it’s working from within the Sonos app. 

Hi Bruce

Apologies for the delay in responding - just wanted to say thank you, that worked!

Thanks for taking the trouble to reply, it’s much appreciated.

Regards

Stephen