Apex domains cannot have CNAME records.
Question and response
Question
dig shareasale.com. NS
Answer
shareasale.com. 4 NS ns-581.awsdns-08.net.
shareasale.com. 4 NS ns-1744.awsdns-26.co.uk.
shareasale.com. 4 NS ns-222.awsdns-27.com.
shareasale.com. 4 NS ns-1496.awsdns-59.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0