Apex domains cannot have CNAME records.
Question and response
Question
dig helpscout.net. NS
Answer
helpscout.net. 5 NS ns-1499.awsdns-59.org.
helpscout.net. 5 NS ns-808.awsdns-37.net.
helpscout.net. 5 NS ns-251.awsdns-31.com.
helpscout.net. 5 NS ns-1550.awsdns-01.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0