Apex domains cannot have CNAME records.
Question and response
Question
dig jan-krueger.biz. NS
Answer
jan-krueger.biz. 5 NS ns3.limenet.de.
jan-krueger.biz. 5 NS ns4.limenet.de.
jan-krueger.biz. 5 NS ns1.limenet.de.
jan-krueger.biz. 5 NS ns2.limenet.de.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0