Apex domains cannot have CNAME records.
Question and response
Question
dig flock.com. NS
Answer
flock.com. 5 NS ns-48.awsdns-06.com.
flock.com. 5 NS ns-1979.awsdns-55.co.uk.
flock.com. 5 NS ns-1219.awsdns-24.org.
flock.com. 5 NS ns-789.awsdns-34.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0