Apex domains cannot have CNAME records.
Question and response
Question
dig gensonline.eu. NS
Answer
gensonline.eu. 5 NS moon.gensonline.eu.
gensonline.eu. 5 NS erde.gensonline.eu.
Authority
The response has no authority records.
Additional
erde.gensonline.eu. 5 A 217.197.85.200
moon.gensonline.eu. 5 A 46.41.1.167
erde.gensonline.eu. 5 AAAA 2001:67c:1407:460:0:0:0:1
moon.gensonline.eu. 5 AAAA 2a02:a00:e00f:fffe:0:0:12:4180
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0