Apex domains cannot have CNAME records.
Question and response
Question
dig 192-255.89.252.125.in-addr.arpa. NS
Answer
192-255.89.252.125.in-addr.arpa. 5 NS ns-1240.awsdns-27.org.
192-255.89.252.125.in-addr.arpa. 5 NS ns-1935.awsdns-49.co.uk.
192-255.89.252.125.in-addr.arpa. 5 NS ns-41.awsdns-05.com.
192-255.89.252.125.in-addr.arpa. 5 NS ns-773.awsdns-32.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0