Apex domains cannot have CNAME records.
Question and response
Question
dig letsignit.com. NS
Answer
letsignit.com. 3 NS ns-43-b.gandi.net.
letsignit.com. 3 NS ns-27-c.gandi.net.
letsignit.com. 3 NS ns-187-a.gandi.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0