Q: Calendar 400 icloud error

Apple support articles.

Calendar Troubleshooting

Calendar and iCal Troubleshooting - Advanced

I also have the error:

The server responded with

“400”

to operation CalDAVAddSubscriptionCalendarQueueableOperation

After trying most if not all of the solutions on the suggested page (including deleting and reloading the calendars from archives) it's still coming up. Is there any other option for fixing? The error is incredibly annoying.

same here. even when I delete everyhting and logout from icloud - don't synch anymore with icloud I will get this error "CalDAVAddSubscriptionCalendarQueueableOperation".

any help?

I had the same problem, and all I had to do was log out of my iCloud account under Internet Accounts, and then log in again on my Mac, so the information can be successfully synced up again.