Google Play Music's death date here in the US is set for just next month. But ahead of that eventual expiration, Google has started shutting down the Music Manager desktop application for managing your Play Music uploads, as it promised earlier this year. A notification going out now tells users that it's no longer available.
One AP tipster that saw the notification received a pop-up forcing them to log back into the app. Subsequently, the notification appeared, explaining that the Music Manager desktop app's days are done. The former download page for Music Manager redirects you to the YouTube Music transfer prompt as well.
Subscribers will want to make sure they've migrated their uploaded songs over to YouTube Music, though keep in mind things don't work exactly the same at the new service. With the Music Manager now dead, you can still probably download your Play Music uploads via Google Takeout, if you need to.