Apex domains cannot have CNAME records.
Question and response
Question
dig 91-web-d.com. NS
Answer
91-web-d.com. 3 NS ns-908.awsdns-49.net.
91-web-d.com. 3 NS ns-472.awsdns-59.com.
91-web-d.com. 3 NS ns-1969.awsdns-54.co.uk.
91-web-d.com. 3 NS ns-1601.awsdns-08.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0