Apex domains cannot have CNAME records.
Question and response
Question
dig AMOCRM.RU. NS
Answer
AMOCRM.RU. 5 NS ns8-l2.nic.RU.
AMOCRM.RU. 5 NS ns4-l2.nic.RU.
AMOCRM.RU. 5 NS ns3-l2.nic.RU.
AMOCRM.RU. 5 NS ns4-cloud.nic.RU.
AMOCRM.RU. 5 NS ns8-cloud.nic.RU.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0