Apex domains cannot have CNAME records.
Question and response
Question
dig keramikrestaurierung.com. NS
Answer
keramikrestaurierung.com. 5 NS ns-1163.awsdns-17.org.
keramikrestaurierung.com. 5 NS ns-1218.awsdns-24.org.
keramikrestaurierung.com. 5 NS ns-113.awsdns-14.com.
keramikrestaurierung.com. 5 NS ns-370.awsdns-46.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0