PS domain.tld is your domain name.

Check the domain entry in below file ,

grep domain.tld /etc/named.conf

if present use /scripts/killdns  domain.tld

grep domain.tld /etc/userdomains

grep domain.tld /usr/local/apache/conf/http.conf

grep domain.tld /etc/localdomains

grep domain.tld /etc/remotedomains

Once your remove the file entry run /scripts/updateuserdomains to sync it.

Done now you can add addon domain .