Apex domains cannot have CNAME records.
Question and response
Question
dig cvent-planner.com. NS
Answer
cvent-planner.com. 5 NS ns-558.awsdns-05.net.
cvent-planner.com. 5 NS ns-1258.awsdns-29.org.
cvent-planner.com. 5 NS ns-1939.awsdns-50.co.uk.
cvent-planner.com. 5 NS ns-168.awsdns-21.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0