Sometimes, you might not able to add the domain that you have remove earlier and wish to re-add it.
To identify the problem, you may check your DNS Zone file, domainusers file, trueuserdomains file, and trueuserowners file.
Remove the domain from file as below.
- /var/named/[domain_name].db (If you used DNS Only cPanel, you may remove zone through WHM).
Once all of the above entry removed, you shall be able to readd your domain name again through cPanel.