Apex domains cannot have CNAME records.
Question and response
Question
dig managedtext.com. NS
Answer
managedtext.com. 2 NS ns-1201.awsdns-22.org.
managedtext.com. 2 NS ns-462.awsdns-57.com.
managedtext.com. 2 NS ns-949.awsdns-54.net.
managedtext.com. 2 NS ns-2027.awsdns-61.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0