If you get error while adding addon domain as below,

————————
Using nameservers with the following IPs: 64.202.165.123,68.178.211.209
Sorry, the domain is already pointed to an IP address that does not
appear to use DNS servers associated with this server. Please transfer
the domain to
this servers nameservers or have your administrator add one of its
nameservers to /etc/ip.remotedns and make the proper A entries on that
remote nameserver.
————————

Then please login into your whm with root login details and goto

WHM > Server Configuration > Tweak Settings > Domians > Allow Creation of Parked/Addon Domains that are not registered.

After saving the changes, you can add the addon domains from your cpanel > addon domain menu.

web hosting service