Apex domains cannot have CNAME records.
Question and response
Question
dig antoniobarbieri.com. NS
Answer
antoniobarbieri.com. 5 NS ns-1855.awsdns-39.co.uk.
antoniobarbieri.com. 5 NS ns-840.awsdns-41.net.
antoniobarbieri.com. 5 NS ns-1282.awsdns-32.org.
antoniobarbieri.com. 5 NS ns-1645.awsdns-13.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0