Apex domains cannot have CNAME records.
Question and response
Question
dig oppay.tw. NS
Answer
oppay.tw. 4 NS dns1.oppay.tw.
oppay.tw. 4 NS dns2.oppay.tw.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0