Apex domains cannot have CNAME records.
Question and response
Question
dig fibraconnect.com.br. NS
Answer
fibraconnect.com.br. 5 NS ns2.fibraconnect.com.br.
fibraconnect.com.br. 5 NS ns1.fibraconnect.com.br.
Authority
The response has no authority records.
Additional
ns1.fibraconnect.com.br. 5 A 168.227.56.10
ns2.fibraconnect.com.br. 5 A 168.227.56.11
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0