Apex domains cannot have CNAME records.
Question and response
Question
dig shimbimybilling.com. NS
Answer
shimbimybilling.com. 5 NS ns2.shimbimybilling.com.
shimbimybilling.com. 5 NS ns1.shimbimybilling.com.
Authority
The response has no authority records.
Additional
ns1.shimbimybilling.com. 5 A 142.44.136.25
ns2.shimbimybilling.com. 5 A 51.222.0.4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0