Apex domains cannot have CNAME records.
Question and response
Question
dig rioguarani.com.br. NS
Answer
rioguarani.com.br. 5 NS ns2-09.azure-dns.net.
rioguarani.com.br. 5 NS ns1-09.azure-dns.com.
rioguarani.com.br. 5 NS ns4-09.azure-dns.info.
rioguarani.com.br. 5 NS ns3-09.azure-dns.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0