Apex domains cannot have CNAME records.
Question and response
Question
dig stspg-customer.com. NS
Answer
stspg-customer.com. 5 NS ns-1711.awsdns-21.co.uk.
stspg-customer.com. 5 NS ns-817.awsdns-38.net.
stspg-customer.com. 5 NS ns-441.awsdns-55.com.
stspg-customer.com. 5 NS ns-1098.awsdns-09.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0