Apex domains cannot have CNAME records.
Question and response
Question
dig activecampaignsd2.com. NS
Answer
activecampaignsd2.com. 5 NS ns-24.awsdns-03.com.
activecampaignsd2.com. 5 NS ns-2021.awsdns-60.co.uk.
activecampaignsd2.com. 5 NS ns-1310.awsdns-35.org.
activecampaignsd2.com. 5 NS ns-750.awsdns-29.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0