It won’t work at the moment, as the Spotify account (set as the default music service) in your Amazon Alexa Account needs to be the exact same account installed on your Sonos system. Note however you can install more than one Spotify account on Sonos setup, via the Sonos App - see this link:
https://support.sonos.com/s/article/3624
Once installed it should then work (all being well), as long as you have installed the ‘Sonos Skill’ in your Alexa App and linked the Sonos Account and Amazon Account and agreed the sharing agreement during the skill setup.
@Ken_Griffiths thank you that is exactly what I was looking for. I did not know you could have two accounts for the same service setup in the Sonos app - that is super convenient