Apex domains cannot have CNAME records.
Question and response
Question
dig highradius.com. NS
Answer
highradius.com. 5 NS ns-401.awsdns-50.com.
highradius.com. 5 NS ns-794.awsdns-35.net.
highradius.com. 5 NS ns-1128.awsdns-13.org.
highradius.com. 5 NS ns-1736.awsdns-25.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0