Apex domains cannot have CNAME records.
Question and response
Question
dig grpleg.net. NS
Answer
grpleg.net. 5 NS var.bticino.it.
grpleg.net. 5 NS ns.grpleg.net.
grpleg.net. 5 NS lim.legrand.tm.fr.
Authority
The response has no authority records.
Additional
ns.grpleg.net. 5 A 212.83.131.113
lim.legrand.tm.fr. 5 A 85.158.16.67
var.bticino.it. 5 A 85.158.16.69
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0