exch.fsi.io has no CNAME records.
Question and response
Question
dig exch.fsi.io. NS
Answer
The response has no answer records.
Authority
fsi.io. 3600 SOA fsi.io. hostmaster.fsi.io. 2026030352 7200 3600 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0