Apex domains cannot have CNAME records.
Question and response
Question
dig customersaas.com. NS
Answer
customersaas.com. 5 NS ns-603.awsdns-11.net.
customersaas.com. 5 NS ns-1964.awsdns-53.co.uk.
customersaas.com. 5 NS ns-254.awsdns-31.com.
customersaas.com. 5 NS ns-1344.awsdns-40.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0