See Share songs from a shared library in Music. If your computer isn’t authorized to play songs purchased by the person who is sharing the song, to hear it you’ll need to enter that person’s Apple ID and password. To listen to a purchased song in a shared library or playlist, double-click the song. If you’re listening to a shared library or playlist: Music skips iTunes Store purchases if your computer hasn’t been authorized to play them. See Usage rights for iTunes Store purchases. If the song is available as an iTunes Plus download, you can upgrade the song at the iTunes Store. (For instructions on deauthorizing a computer, see Authorize a Mac to play iTunes Store purchases.) After you authorize five computers, you can’t play the songs on a sixth computer until you deauthorize one of the five authorized computers. If the song isn’t an iTunes Plus version, you can play it on up to five authorized computers. If you can’t play a song purchased from the iTunes Store: You may have exceeded the number of computers on which you can play your purchases.
