Apex domains cannot have CNAME records.
Question and response
Question
dig greenlineswiss-ag.com. NS
Answer
greenlineswiss-ag.com. 5 NS ns-81.awsdns-10.com.
greenlineswiss-ag.com. 5 NS ns-52.awsdns-06.com.
greenlineswiss-ag.com. 5 NS ns-884.awsdns-46.net.
greenlineswiss-ag.com. 5 NS ns-352.awsdns-44.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0