Apex domains cannot have CNAME records.
Question and response
Question
dig cust.key-sol.net. NS
Answer
cust.key-sol.net. 1 NS pns53.cloudns.net.
cust.key-sol.net. 1 NS pns54.cloudns.net.
cust.key-sol.net. 1 NS pns51.cloudns.net.
cust.key-sol.net. 1 NS pns52.cloudns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0