Apex domains cannot have CNAME records.
Question and response
Question
dig dns40.com. NS
Answer
dns40.com. 1 NS vera.ns.cloudflare.com.
dns40.com. 1 NS matt.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0