Apex domains cannot have CNAME records.
Question and response
Question
dig ds.synergy-learning.com. NS
Answer
ds.synergy-learning.com. 5 NS ns-1226.awsdns-25.org.
ds.synergy-learning.com. 5 NS ns-1805.awsdns-33.co.uk.
ds.synergy-learning.com. 5 NS ns-54.awsdns-06.com.
ds.synergy-learning.com. 5 NS ns-992.awsdns-60.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0