Apex domains cannot have CNAME records.
Question and response
Question
dig certto.com.br. NS
Answer
certto.com.br. 5 NS ns2.certto.com.br.
certto.com.br. 5 NS ns1.certto.com.br.
Authority
The response has no authority records.
Additional
ns1.certto.com.br. 5 A 186.251.148.23
ns2.certto.com.br. 5 A 186.251.148.24
ns1.certto.com.br. 5 AAAA 2804:1cc:ffff:ffc0:0:0:0:23
ns2.certto.com.br. 5 AAAA 2804:1cc:ffff:ffc0:0:0:0:24
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0