Apex domains cannot have CNAME records.
Question and response
Question
dig zantrevoxil.com. NS
Answer
zantrevoxil.com. 5 NS ns-505.awsdns-63.com.
zantrevoxil.com. 5 NS ns-1694.awsdns-19.co.uk.
zantrevoxil.com. 5 NS ns-1252.awsdns-28.org.
zantrevoxil.com. 5 NS ns-525.awsdns-01.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0