Apex domains cannot have CNAME records.
Question and response
Question
dig 103-16-231-240.warm.eu.com. NS
Answer
103-16-231-240.warm.eu.com. 5 NS dns102.registrar-servers.com.
103-16-231-240.warm.eu.com. 5 NS dns101.registrar-servers.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0