Apex domains cannot have CNAME records.
Question and response
Question
dig 0-63.129.84.62.in-addr.arpa. NS
Answer
0-63.129.84.62.in-addr.arpa. 5 NS ns1.gts.cz.
0-63.129.84.62.in-addr.arpa. 5 NS ns2.gts.cz.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0