Apex domains cannot have CNAME records.
Question and response
Question
dig fsi.io. NS
Answer
fsi.io. 5 NS ns6.dnsmadeeasy.com.
fsi.io. 5 NS ns7.dnsmadeeasy.com.
fsi.io. 5 NS ns5.dnsmadeeasy.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0