Apex domains cannot have CNAME records.
Question and response
Question
dig n-able.com. NS
Answer
n-able.com. 5 NS ns-447.awsdns-55.com.
n-able.com. 5 NS ns-571.awsdns-07.net.
n-able.com. 5 NS ns-1243.awsdns-27.org.
n-able.com. 5 NS ns-1706.awsdns-21.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0