Apex domains cannot have CNAME records.
Question and response
Question
dig bitrix24.com. NS
Answer
bitrix24.com. 5 NS ns-572.awsdns-07.net.
bitrix24.com. 5 NS ns-439.awsdns-54.com.
bitrix24.com. 5 NS ns-1745.awsdns-26.co.uk.
bitrix24.com. 5 NS ns-1377.awsdns-44.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0