Apex domains cannot have CNAME records.
Question and response
Question
dig ergovia.de. NS
Answer
ergovia.de. 2 NS ns1044.ui-dns.biz.
ergovia.de. 2 NS ns1044.ui-dns.de.
ergovia.de. 2 NS ns1044.ui-dns.org.
ergovia.de. 2 NS ns1044.ui-dns.com.
Authority
The response has no authority records.
Additional
ns1044.ui-dns.de. 4 A 217.160.80.44
ns1044.ui-dns.biz. 4 A 217.160.81.44
ns1044.ui-dns.com. 4 A 217.160.82.44
ns1044.ui-dns.org. 4 A 217.160.83.44
ns1044.ui-dns.de. 4 AAAA 2001:8d8:fe:53:0:d9a0:502c:100
ns1044.ui-dns.biz. 4 AAAA 2001:8d8:fe:53:0:d9a0:512c:100
ns1044.ui-dns.com. 4 AAAA 2001:8d8:fe:53:0:d9a0:522c:100
ns1044.ui-dns.org. 4 AAAA 2001:8d8:fe:53:0:d9a0:532c:100
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0