Apex domains cannot have CNAME records.
Question and response
Question
dig jetsmtp.io. NS
Answer
jetsmtp.io. 5 NS melina.ns.cloudflare.com.
jetsmtp.io. 5 NS yisroel.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0