Apex domains cannot have CNAME records.
Question and response
Question
dig clientpay.com. NS
Answer
clientpay.com. 5 NS ns-1670.awsdns-16.co.uk.
clientpay.com. 5 NS ns-596.awsdns-10.net.
clientpay.com. 5 NS ns-464.awsdns-58.com.
clientpay.com. 5 NS ns-1333.awsdns-38.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0