I will assume you are using a mobile device compatible controller, as mentioned in this Sonos support link:

https://support.sonos.com/en-us/article/sonos-app-requirements

If so, then my thoughts are to perhaps try a different DNS server in your router configuration. Perhaps use Google (8.8.8.8/8.8.4.4), or Cloudflare (1.1.1.1) public DNS servers and see if that solves it for you. 
 

If you’re not sure about the password etc; you could also reset the password or transfer the Sonos system to your known Sonos account credentials.

See these two links, which hopefully may assist:

• https://support.sonos.com/en-us/article/change-or-reset-your-sonos-account-password
• https://support.sonos.com/en-us/article/transfer-your-sonos-system-to-a-new-account

Thanks Ken! 
I use a mobile device - iPhone XS Max - iOS 16.5
I remember the password but can’t even get to page where I supposed to type it
And we already checked the DNS.

Maybe try a Sonos App reset from ‘Settings/App Preferences’ and see if that might resolve the issue - on reopening the App, accept the T&C’s and connect it back to the existing Sonos system. 

Hi @gilm 

Welcome to the Sonos Community!

If you are still experiencing this issue, I recommend you get in touch with our technical support team who have tools at their disposal that will allow them to give you advice specific to your Sonos system and what it reports.

I hope this helps.