When I am trying to add a site via add new site its throws error as following “The zone name provided is subject to a hold which disallows the creation of this zone. Please contact the domain owner to have this hold removed.”
This means the domain is active on an existing Enterprise account and they disallow it being added to other accounts. As it says in the error you can contact the domain owner. If you own the domain you can change the nameservers away from their Cloudflare account to try and force deactivate their zone. If those approaches are not viable you may contact support.
After adding the record you need to reply back to support and tell them such. They will then proceed.