Apex domains cannot have CNAME records.
Question and response
Question
dig dynamic.3bb.co.th. NS
Answer
dynamic.3bb.co.th. 5 NS ns2.dynamic.3bb.co.th.
dynamic.3bb.co.th. 5 NS ns1.dynamic.3bb.co.th.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0