Apex domains cannot have CNAME records.
Question and response
Question
dig 96-111.218.36.138.in-addr.arpa. NS
Answer
96-111.218.36.138.in-addr.arpa. 5 NS ns-167.awsdns-20.com.
96-111.218.36.138.in-addr.arpa. 5 NS ns-556.awsdns-05.net.
96-111.218.36.138.in-addr.arpa. 5 NS ns-1161.awsdns-17.org.
96-111.218.36.138.in-addr.arpa. 5 NS ns-1839.awsdns-37.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0