failed pointing foo2.com (customer) to mainfoo.com hosting

hello.
i already create mainfoo.com and already set DNS Zone
ns1.mainfoo.com and ns2.mainfoo.com
i ping from outside (not server) is solved
but when i ping from ssh (server) unknown but i can ping the public ip

then i try to add foo2.com
with NS pointing to:
ns1.mainfoo.com
ns2.mainfoo.com
result not solved

but if i put IN A… then it solved

the next case are… when i open the foo2.com dns zone… it empty
no Zone template there