Apex domains cannot have CNAME records.
Question and response
Question
dig radicenter.com. NS
Answer
radicenter.com. 5 NS ns3.radicenter.ee.
radicenter.com. 5 NS ns2.radicenter.eu.
radicenter.com. 5 NS ns1.radicenter.com.
radicenter.com. 5 NS ns4.radicenter.fi.
Authority
The response has no authority records.
Additional
ns1.radicenter.com. 5 A 185.86.211.11
ns1.radicenter.com. 5 AAAA 2a13:c5c0:dc1:0:0:0:0:11
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0