Apex domains cannot have CNAME records.
Question and response
Question
dig jm-data.at. NS
Answer
jm-data.at. 5 NS dns2.jm-data.at.
jm-data.at. 5 NS dns3.jm-data.at.
jm-data.at. 5 NS dns1.jm-data.at.
Authority
The response has no authority records.
Additional
dns1.jm-data.at. 5 A 217.16.112.21
dns2.jm-data.at. 5 A 217.16.112.22
dns3.jm-data.at. 5 A 62.93.70.3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0