Apex domains cannot have CNAME records.
Question and response
Question
dig scb.co.th. NS
Answer
scb.co.th. 5 NS ns-1220.awsdns-24.org.
scb.co.th. 5 NS ns-931.awsdns-52.net.
scb.co.th. 5 NS ns-346.awsdns-43.com.
scb.co.th. 5 NS ns-1944.awsdns-51.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0