Apex domains cannot have CNAME records.
Question and response
Question
dig 0-63.123.73.109.in-addr.arpa. NS
Answer
0-63.123.73.109.in-addr.arpa. 5 NS ns0.beepweb.net.
0-63.123.73.109.in-addr.arpa. 5 NS ns1.beepweb.net.
Authority
The response has no authority records.
Additional
ns0.beepweb.net. 5 A 109.73.123.38
ns1.beepweb.net. 5 A 213.129.83.251
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0