Apex domains cannot have CNAME records.
Question and response
Question
dig nexxera.com.br. NS
Answer
nexxera.com.br. 5 NS ns-647.awsdns-16.net.
nexxera.com.br. 5 NS ns-322.awsdns-40.com.
nexxera.com.br. 5 NS ns003.nexxera.com.br.
nexxera.com.br. 5 NS ns-1964.awsdns-53.co.uk.
Authority
The response has no authority records.
Additional
ns003.nexxera.com.br. 5 A 189.124.62.10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0