Apex domains cannot have CNAME records.
Question and response
Question
dig 0-25.48.19.206.in-addr.arpa. NS
Answer
0-25.48.19.206.in-addr.arpa. 5 NS ns1-05.azure-dns.com.
0-25.48.19.206.in-addr.arpa. 5 NS ns2-05.azure-dns.net.
0-25.48.19.206.in-addr.arpa. 5 NS ns3-05.azure-dns.org.
0-25.48.19.206.in-addr.arpa. 5 NS ns4-05.azure-dns.info.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0