Apex domains cannot have CNAME records.
Question and response
Question
dig mathieu-callet.com. NS
Answer
mathieu-callet.com. 5 NS ns-908.awsdns-49.net.
mathieu-callet.com. 5 NS ns-1560.awsdns-03.co.uk.
mathieu-callet.com. 5 NS ns-858.awsdns-43.net.
mathieu-callet.com. 5 NS ns-932.awsdns-52.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0