Apex domains cannot have CNAME records.
Question and response
Question
dig zap.cloud. NS
Answer
zap.cloud. 2 NS ns1.zap-hosting.com.
zap.cloud. 2 NS ns2.zap-hosting.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0