Apex domains cannot have CNAME records.
Question and response
Question
dig retarus.com. NS
Answer
retarus.com. 5 NS ns-1712.awsdns-22.co.uk.
retarus.com. 5 NS ns-732.awsdns-27.net.
retarus.com. 5 NS ns-83.awsdns-10.com.
retarus.com. 5 NS ns-1452.awsdns-53.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0