Apex domains cannot have CNAME records.
Question and response
Question
dig clearfly.io. NS
Answer
clearfly.io. 5 NS ns1.as27400.net.
clearfly.io. 5 NS ns3.as27400.net.
clearfly.io. 5 NS ns2.as27400.net.
Authority
The response has no authority records.
Additional
ns1.as27400.net. 5 A 208.85.60.5
ns2.as27400.net. 5 A 208.85.60.6
ns3.as27400.net. 5 A 107.170.248.223
ns1.as27400.net. 5 AAAA 2607:f3d0:0:1:0:0:0:5
ns2.as27400.net. 5 AAAA 2607:f3d0:0:2:0:0:0:5
ns3.as27400.net. 5 AAAA 2604:a880:1:20:0:0:2f:d001
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0