o2.sg.calendly.com has no NS records.
NS records for this zone are defined at calendly.com.
NS records for this zone are defined at calendly.com.
Question and response
Question
dig o2.sg.calendly.com. NS
Answer
The response has no answer records.
Authority
calendly.com. 1800 SOA hope.ns.cloudflare.com. dns.cloudflare.com. 2398134940 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0