Apex domains cannot have CNAME records.
Question and response
Question
dig sixent.com. NS
Answer
sixent.com. 5 NS ns-1195.awsdns-21.org.
sixent.com. 5 NS ns-73.awsdns-09.com.
sixent.com. 5 NS ns-811.awsdns-37.net.
sixent.com. 5 NS ns-2010.awsdns-59.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0