Apex domains cannot have CNAME records.
Question and response
Question
dig stackhero-network.com. NS
Answer
stackhero-network.com. 5 NS dns-czp3l1.stackhero.io.
stackhero-network.com. 5 NS dns-frepms.stackhero.io.
stackhero-network.com. 5 NS dns-usw1za.stackhero.io.
stackhero-network.com. 5 NS dns-ams1zm.stackhero.io.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0