Apex domains cannot have CNAME records.
Question and response
Question
dig customerly.io. NS
Answer
customerly.io. 5 NS ns-1435.awsdns-51.org.
customerly.io. 5 NS ns-171.awsdns-21.com.
customerly.io. 5 NS ns-884.awsdns-46.net.
customerly.io. 5 NS ns-1905.awsdns-46.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0