Apex domains cannot have CNAME records.
Question and response
Question
dig 224-27.226.104.184.in-addr.arpa. NS
Answer
224-27.226.104.184.in-addr.arpa. 5 NS ns59.tophost.ch.
224-27.226.104.184.in-addr.arpa. 5 NS ns60.tophost.ch.
Authority
The response has no authority records.
Additional
ns59.tophost.ch. 5 A 193.33.128.37
ns60.tophost.ch. 5 A 184.104.226.229
ns59.tophost.ch. 5 AAAA 2a02:6201:c121:8020:0:0:25:1
ns60.tophost.ch. 5 AAAA 2001:470:77:0:0:0:e5:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0