Apex domains cannot have CNAME records.
Question and response
Question
dig insmartcloud.com. NS
Answer
insmartcloud.com. 5 NS ns-350.awsdns-43.com.
insmartcloud.com. 5 NS ns-1193.awsdns-21.org.
insmartcloud.com. 5 NS ns-888.awsdns-47.net.
insmartcloud.com. 5 NS ns-1846.awsdns-38.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0