Apex domains cannot have CNAME records.
Question and response
Question
dig onapp.ip-only.net. NS
Answer
onapp.ip-only.net. 5 NS ns3.onapp.ip-only.net.
onapp.ip-only.net. 5 NS ns1.onapp.ip-only.net.
onapp.ip-only.net. 5 NS ns2.onapp.ip-only.net.
onapp.ip-only.net. 5 NS ns4.onapp.ip-only.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0