When i try to enable iCloud Sync, for example, using 1Password.app i have an error saying "The Operation couldn't be completed. (CKErrorDomain error 7.)" or "Request failed with http status code 503". I have this issue with all the apps i have installed with "iCloud Sync" feature on any device with iOS 9.3 beta 4.
Error activating "iCloud Sync" (3rd. party apps)
I got this too - but I'm not running any Beta software - I'm on 9.2.1.
Looks more like an iCloud issue - as anything with iCloud syncing doesn't seem to be working. My photos app stopped syncing.
Got this error on my Macs too
Mac mini
Request failed with http status code 503
Macbook Pro
The operation couldn’t be completed. (CKErrorDomain error 7.)
also not on Mac beta, but the iPhone is running the 9.3 beta 4
I recognized also that the Notes.app stops syncing via iCloud, seemed that this is a major iCloud problem.
1Password told me that "Last sync: 4 days ago", since installation of iOS 9.3 beta 4