A couple of thoughts. 

First, go in and look at your account settings at www.Sonos.com, paying particular attention to the location specified on the account. Sonos does some filtering based on some portion of that data, so if the country and post code (and maybe city? I’m not sure) isn’t set, you may have some difficulties.

The second possibility is your network may just need a refresh, to ensure it is working/connecting properly. Try unplugging all Sonos devices from power, then reboot your router. When the router comes back up, plug the Sonos devices back in. 

I suppose there’s always the possibility of either a VPN or firewall blocking the speaker’s ability to reach the Sonos servers to add the service, so if neither of the above don’t work, I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it, or post the diagnostic number here for a Community Moderator to pick up.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the phone folks, there are more options available beyond just the diagnostic analysis. 

There is a (small) finite limit to the number of Favorites you can add (which is the tech under “My Sonos”). I can’t recall the exact number, but I think its around 40. To tell if you have hit the limit try deleting one and adding one, if that works then you have hit the limit.

It may also depend on what “something” is.

Same problem for me. I only have 19 items in my “Sonos Favorites” (as shown on Sonos S1 controller on my Mac) and only 7 items in “My Sonos” - “Songs” (as shown on my iPhone Sonos S1 app. Can’t add songs or stations regardless of whether they’re from YouTube Music, Amazon Music, iHeartRadio, etc.