Apex domains cannot have CNAME records.
Question and response
Question
dig grupojet.com.br. NS
Answer
grupojet.com.br. 5 NS corey.ns.cloudflare.com.
grupojet.com.br. 5 NS reza.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0