Apex domains cannot have CNAME records.
Question and response
Question
dig fucloud.de. NS
Answer
fucloud.de. 3 NS ns1.first-ns.de.
fucloud.de. 3 NS robotns3.second-ns.com.
fucloud.de. 3 NS robotns2.second-ns.de.
Authority
The response has no authority records.
Additional
ns1.first-ns.de. 4 A 213.239.242.238
robotns2.second-ns.de. 4 A 213.133.100.103
robotns3.second-ns.com. 4 A 193.47.99.3
ns1.first-ns.de. 4 AAAA 2a01:4f8:0:a101:0:0:a:1
robotns2.second-ns.de. 4 AAAA 2a01:4f8:0:1:0:0:5ddc:2
robotns3.second-ns.com. 4 AAAA 2001:67c:192c:0:0:0:add:a3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0