Apex domains cannot have CNAME records.
Question and response
Question
dig rpanel.io. NS
Answer
rpanel.io. 5 NS a.ns.joker.com.
rpanel.io. 5 NS c.ns.joker.com.
rpanel.io. 5 NS b.ns.joker.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0