I can't play songs on apple music

Apologies, this line is only relevant on Windows machines.

If so try Edit > Preferences > Devices > Reset Sync History (if available) and then try syncing once more.

tt2

Is this on your Mac or an iOS device?

If so try Edit > Preferences > Devices > Reset Sync History (if available) and then try syncing once more.

If that hasn't helped try signing out of the iTunes Store on the device and then try again.

Otherwise see this post on erratic syncing.

tt2

Where should I edit it ?