Apex domains cannot have CNAME records.
Question and response
Question
dig contabo.net. NS
Answer
contabo.net. 5 NS ns3.contabo.net.
contabo.net. 5 NS ns2.contabo.net.
contabo.net. 5 NS ns1.contabo.net.
Authority
The response has no authority records.
Additional
ns1.contabo.net. 5 A 5.180.150.13
ns2.contabo.net. 5 A 195.179.224.10
ns3.contabo.net. 5 A 209.126.15.15
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0