Apex domains cannot have CNAME records.
Question and response
Question
dig pavietnam.com. NS
Answer
pavietnam.com. 4 NS dns1.pavietnam.com.
pavietnam.com. 4 NS dns2.pavietnam.com.
Authority
The response has no authority records.
Additional
dns1.pavietnam.com. 4 A 147.182.227.22
dns2.pavietnam.com. 4 A 146.190.14.198
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0