Apex domains cannot have CNAME records.
Question and response
Question
dig sprintervals.com. NS
Answer
sprintervals.com. 5 NS ns-847.awsdns-41.net.
sprintervals.com. 5 NS ns-1986.awsdns-56.co.uk.
sprintervals.com. 5 NS ns-299.awsdns-37.com.
sprintervals.com. 5 NS ns-1780.awsdns-30.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0