Apex domains cannot have CNAME records.
Question and response
Question
dig e-invoice.com. NS
Answer
e-invoice.com. 5 NS konnor.ns.cloudflare.com.
e-invoice.com. 5 NS paloma.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0