Apex domains cannot have CNAME records.
Question and response
Question
dig ftpi.or.th. NS
Answer
ftpi.or.th. 5 NS pete.ns.cloudflare.com.
ftpi.or.th. 5 NS venus.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0