I assume you are playing from the same service and account?  If so, a single account will not play on 2 separate systems at the same time.   The music services limit the number of streams to each IP address to prevent account sharing. 

Two different accounts but both do use my Spotify

If both are your username/password, then Spotify will prevent two or more streams on any system(s) at once.  You need a Spotify Family plan and then add all accounts to the Sonos controller.  See this link:

https://support.sonos.com/en-us/article/use-multiple-accounts-for-the-same-content-service

Thank you. I will try this.

Just to make it clear: this is a Spotify problem, not a Sonos problem.

So it seems, yes.

Update: i got Spotify Duo and everything works now.

But what is really weird, is that my wife had got another premium order back in a day without me knowing and it was in use. So that did not work obviously for the problem ai had. But when Spotify asked the address for duo it started working right away. Even though the premium of hers was still in use and the duo account was just only made but not signed into yet.

I am at loss... But glad it works now