Apex domains cannot have CNAME records.
Question and response
Question
dig cdkmessaging.com. NS
Answer
cdkmessaging.com. 5 NS ns-234.awsdns-29.com.
cdkmessaging.com. 5 NS ns-1877.awsdns-42.co.uk.
cdkmessaging.com. 5 NS ns-1128.awsdns-13.org.
cdkmessaging.com. 5 NS ns-592.awsdns-10.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0