How do you solve the iTunes error 4002?

Answer 1

Update Mac OS from the apple icon in the top left corner of your screen, then go into iTunes and update available Apps.

From the iTunes menu bar select Store and then turn Off and then On Genius.

If not repaired, reinstall iTunes.

Answer 2

It's a server side error. Nothing you can do but potentially report it to Apple (or even better to the vendor).