Why won’t iTunes authorize my computer? The most common problem with not being able to authorize a computer is that you have too many of them already authorized. Due to licensing agreements, you can only have a maximum of five computers authorized under your iTunes account at the same time.
How do I Authorise a computer for iTunes on a Mac? Authorise a computer to play iTunes Store purchases
In the Music app on your Mac, choose Account > Authorisations > Authorise This Computer. If requested, enter your Apple ID password to confirm.
How do I authorize a computer for music?
How do I authorize my computer? To authorize your Windows computer, open the iTunes app and click Account in the menu bar. Then click Sign In and enter your Apple ID and password. Next, click Account again and hover over Authorizations and select Authorize This Computer. Open the iTunes app on your Windows 10 computer.