Describe your setup. I’m assuming you have a music library in iTunes on a Mac. Have you set up the music library in the Sonos app? Are you saying that when you “Update Music Index Now” in the Sonos app, new albums that you have just added to your iTunes music library don’t appear in the Sonos app? Are these albums you purchased from iTunes or albums ripped from CDs? What does “for the first time” mean?

I have had Sonos for a few years and have always been able to add to the music library whenever I purchase a new cd and load it into my iTunes on my MacBook… until today.

What version of macOS are you using? Have you updated it recently? What happens when you update the music index in the Sonos app? Have you tried rebooting your MacBook, phone, and router?

How big is your music collection? Have you reached the maximum tracks limit?

I see there’s another thread here 

Is this the same problem, @Kajack ?

My MacBook is old.  I have High Sierra 10.13.6 and am told I can’t do any more upgrades.  My library has about 86 albums, don’t know how to tell how many songs or what the limit is.  I have rebooted everything.  When I try to add a new album it says my iTunes is no longer available and to check the path.  I can’t find anything to change.  I have always been able to add new albums to Sonos before.

Do you use Dropbox? Problem and solution here:

I have the free version of Dropbox.  Does it have the capacity?

No idea; I’m not using it. But the final post on that link said, “I went into iTunes and checked the file paths of the recently added songs that were not showing up in Sonos, and found that they were different. A couple of weeks earlier I had started syncing all my folders with Dropbox under some new super sync program they have, and dropbox had somehow hijacked the file path so that it started ////dropbox/// etc etc.”  Have you checked your paths?

Not sure how to check paths.

The same way you set up your library to start with. Go to Settings, System, Music Library, Music Library Setup and check the details. Correct them if necessary. 

In Music Library Setup I have an iTunes folder and a Music folder.  Neither opens to show me the path or anything else.

What does it show for those two folders in Music Library Setup?