Apex domains cannot have CNAME records.
Question and response
Question
dig teamwork.com. NS
Answer
teamwork.com. 2 NS ns-1319.awsdns-36.org.
teamwork.com. 2 NS ns-67.awsdns-08.com.
teamwork.com. 2 NS ns-743.awsdns-28.net.
teamwork.com. 2 NS ns-1985.awsdns-56.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0