Apex domains cannot have CNAME records.
Question and response
Question
dig omantel.net.om. NS
Answer
omantel.net.om. 5 NS stephane.ns.cloudflare.com.
omantel.net.om. 5 NS ivan.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0