Apex domains cannot have CNAME records.
Question and response
Question
dig bamboo-demo.ivcert.net. NS
Answer
bamboo-demo.ivcert.net. 5 NS ns-1635.awsdns-12.co.uk.
bamboo-demo.ivcert.net. 5 NS ns-663.awsdns-18.net.
bamboo-demo.ivcert.net. 5 NS ns-39.awsdns-04.com.
bamboo-demo.ivcert.net. 5 NS ns-1488.awsdns-58.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0