Apex domains cannot have CNAME records.
Question and response
Question
dig resend.com. NS
Answer
resend.com. 3 NS ns-399.awsdns-49.com.
resend.com. 3 NS ns-1047.awsdns-02.org.
resend.com. 3 NS ns-1017.awsdns-63.net.
resend.com. 3 NS ns-1910.awsdns-46.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0