Apex domains cannot have CNAME records.
Question and response
Question
dig demo.ivcert.net. NS
Answer
demo.ivcert.net. 5 NS ns-1644.awsdns-13.co.uk.
demo.ivcert.net. 5 NS ns-101.awsdns-12.com.
demo.ivcert.net. 5 NS ns-709.awsdns-24.net.
demo.ivcert.net. 5 NS ns-1389.awsdns-45.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0