What is error 502 in iTunes

Error 502 is usually related to conflicts with third party security software. Read the article for troubleshooting steps.

If you see 'There was an error downloading your purchased music' when you try to download music from iTunes - Apple Supp…

I started to get this for the first time tonight when iTunes 12.4.3.1 (on 10.11.6) refused to download updates to Apps.

The fault disappeared after 24 hours; apart from the long-standing bug where the badge in iOS fails to reflect apps updated via the desktop, iTunes is functioning normally now.