The official System Status page for all Apple’s services shows that three of the most important ones are having problems The iOS App Store, the Mac App Store and the iTunes Store are all affected.
Many of the people using these three stores may find that they can’t actually buy anything. “Customers may be unable to make purchases from the App Store, iTunes Store, Apple Books, or Mac App Store,” reads the note on the official System Status page.
The page also notes that “Some users are affected,” so the issue isn’t universal. How many people can’t complete their purchases is unknown at this time.
This problem has been going on for several hours now. Apple hasn’t announced what the source is, nor given an estimate on when it will be fixed.