Apex domains cannot have CNAME records.
Question and response
Question
dig onappcdn.com. NS
Answer
onappcdn.com. 5 NS dns43.cloudns.net.
onappcdn.com. 5 NS ns2.he.net.
onappcdn.com. 5 NS ns3.he.net.
onappcdn.com. 5 NS dns41.cloudns.net.
onappcdn.com. 5 NS dns42.cloudns.net.
onappcdn.com. 5 NS dns44.cloudns.net.
Authority
The response has no authority records.
Additional
ns2.he.net. 5 A 216.218.131.2
ns3.he.net. 5 A 216.218.132.2
ns2.he.net. 5 AAAA 2001:470:200:0:0:0:0:2
ns3.he.net. 5 AAAA 2001:470:300:0:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0