Prevent Clients from Signing Up with Domains That Already Have an Entry in the cPanel DNS Cluster
This error sometimes occurs after a customer pays for hosting:
Order Accept Encountered Problems
Sorry, a DNS entry for example.com already exists, please delete it first (from all servers in the DNS cluster)
WHMCS could see into the DNS cluster it could prevent a customer from
paying if they used a domain that already exists in the cPanel cluster.