Apex domains cannot have CNAME records.
Question and response
Question
dig network.k.io. NS
Answer
network.k.io. 5 NS ns2.katapult.io.
network.k.io. 5 NS ns1.katapult.io.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0