Apex domains cannot have CNAME records.
Question and response
Question
dig pc021.co.rs. NS
Answer
pc021.co.rs. 5 NS dave.ns.cloudflare.com.
pc021.co.rs. 5 NS zoe.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0