Apex domains cannot have CNAME records.
Question and response
Question
dig api-2mail.xyz. NS
Answer
api-2mail.xyz. 5 NS ns64.domaincontrol.com.
api-2mail.xyz. 5 NS ns63.domaincontrol.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0