Apex domains cannot have CNAME records.
Question and response
Question
dig iagentedns.com.br. NS
Answer
iagentedns.com.br. 5 NS ns2.iagentedns.com.br.
iagentedns.com.br. 5 NS ns4.iagentedns.com.br.
iagentedns.com.br. 5 NS ns5.iagentends.com.br.
iagentedns.com.br. 5 NS ns1.iagentedns.com.br.
iagentedns.com.br. 5 NS ns3.iagentedns.com.br.
Authority
The response has no authority records.
Additional
ns1.iagentedns.com.br. 5 A 177.85.210.12
ns2.iagentedns.com.br. 5 A 177.85.210.13
ns3.iagentedns.com.br. 5 A 177.85.210.14
ns4.iagentedns.com.br. 5 A 159.203.170.213
ns1.iagentedns.com.br. 5 AAAA 2804:6f8:0:1:177:85:210:12
ns2.iagentedns.com.br. 5 AAAA 2804:6f8:0:1:177:85:210:13
ns3.iagentedns.com.br. 5 AAAA 2804:6f8:0:1:177:85:210:14
ns4.iagentedns.com.br. 5 AAAA 2604:a880:800:14:0:0:6d52:f000
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0