not able to add icloud account

Hey, Thanks for reaching out to us.

Please navigate to iOS->Advanced Restrictions->Allow Security and Privacy Settings and confirm that the ‘Modify an account’ option is enabled.
When the option is not enabled, you would not be able to add/remove an account or change password of the accounts. The modification of app account from the device settings will also be blocked when this option is disabled. Please associate targets and save the policy once the option is enabled.
Click here to get more insights into restrictions for iOS devices.

Hope this helps. Please contact us for any further queries.

Cheers!
Grace Baker
Hexnode MDM