Apex domains cannot have CNAME records.
Question and response
Question
dig extole.io. NS
Answer
extole.io. 5 NS ns-603.awsdns-11.net.
extole.io. 5 NS ns-231.awsdns-28.com.
extole.io. 5 NS ns-1510.awsdns-60.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0