oifm-api.oi.com.br has no NS records.
NS records for this zone are defined at oi.com.br.
NS records for this zone are defined at oi.com.br.
Question and response
Question
dig oifm-api.oi.com.br. NS
Answer
The response has no answer records.
Authority
oi.com.br. 300 SOA ns01.oi.net.br. hostmaster.oi.com.br. 414275585 600 1800 604800 300
Additional
. 0 OPT ; payload 4000, xrcode 0, version 0, flags 0