Apex domains cannot have CNAME records.
Question and response
Question
dig lag-arbeit-hessen.net. NS
Answer
lag-arbeit-hessen.net. 5 NS ns-538.awsdns-03.net.
lag-arbeit-hessen.net. 5 NS ns-1296.awsdns-34.org.
lag-arbeit-hessen.net. 5 NS ns-424.awsdns-53.com.
lag-arbeit-hessen.net. 5 NS ns-506.awsdns-63.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0