Apex domains cannot have CNAME records.
Question and response
Question
dig bigcommerce.com. NS
Answer
bigcommerce.com. 5 NS ns-cloud-d1.googledomains.com.
bigcommerce.com. 5 NS ns-cloud-d3.googledomains.com.
bigcommerce.com. 5 NS dns2.p01.nsone.net.
bigcommerce.com. 5 NS ns-cloud-d2.googledomains.com.
Authority
The response has no authority records.
Additional
dns2.p01.nsone.net. 5 A 198.51.45.1
dns2.p01.nsone.net. 5 AAAA 2a00:edc0:6259:7:1:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0