CAA records in the domain's zone file restrict which CAs (Certificate Authority) may issue certificates for that domain. If no CAA records exist for a domain, all CAs can issue certificates for that domain. If conflicting CAA records already exist, remove the existing CAA records or add one for the desired CA. For example, a CAA record for Comodo would resemble the following example, where
example.com represents the domain name:
example.com. 86400 IN CAA 0 issue "comodoca.com"
You can manage CAA records through WHM's Edit DNS Zone interface (WHM >> Home >> DNS Functions >> Edit DNS Zone) or through cPanel's Zone Editor interface (cPanel >> Home >> Domains >> Zone Editor).
For more information about a CA's requirements, read their documentation.