Apex domains cannot have CNAME records.
Question and response
Question
dig singtelmybusiness.com. NS
Answer
singtelmybusiness.com. 5 NS ns-383.awsdns-47.com.
singtelmybusiness.com. 5 NS ns-1434.awsdns-51.org.
singtelmybusiness.com. 5 NS ns-528.awsdns-02.net.
singtelmybusiness.com. 5 NS ns-1790.awsdns-31.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0