Apex domains cannot have CNAME records.
Question and response
Question
dig cartstack.com. NS
Answer
cartstack.com. 4 NS ns-1538.awsdns-00.co.uk.
cartstack.com. 4 NS ns-301.awsdns-37.com.
cartstack.com. 4 NS ns-617.awsdns-13.net.
cartstack.com. 4 NS ns-1175.awsdns-18.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0