Apex domains cannot have CNAME records.
Question and response
Question
dig psa.at. NS
Answer
psa.at. 4 NS ns2.psa-services.net.
psa.at. 4 NS ns4.psa-services.net.
psa.at. 4 NS ns1.psa-services.net.
psa.at. 4 NS ns3.psa-services.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0