_ExcerptLicenseAndPermissions

You can only change user's license from Supervisor to Admin, if you are an admin user.

If you change a user's license from Supervisor to Admin, the permissions settings section disappears; permission settings are not relevant for admin users. However, Vonage Contact Center does not delete the actual permissions even when you save the license change. If you later change the user's license back from Admin to Supervisor, the permission settings section reappears. The previously saved permissions do not appear until you save the user again. If you add any permissions without saving the user first, when you do save the user, your new permissions overwrite the original permission settings.

The same applies when changing multiple users' licenses from Supervisor to Admin using bulk actions.