Apex domains cannot have CNAME records.
Question and response
Question
dig saasplaza.sg. NS
Answer
saasplaza.sg. 5 NS ns4.saasplaza.us.
saasplaza.sg. 5 NS ns3.saasplaza.us.
saasplaza.sg. 5 NS ns1.saasplaza.com.
saasplaza.sg. 5 NS ns3.saasplaza.sg.
saasplaza.sg. 5 NS ns2.saasplaza.com.
saasplaza.sg. 5 NS ns4.saasplaza.sg.
Authority
The response has no authority records.
Additional
ns1.saasplaza.com. 5 A 20.54.224.234
ns2.saasplaza.com. 5 A 20.61.245.70
ns3.saasplaza.sg. 5 A 172.188.98.61
ns3.saasplaza.us. 5 A 198.181.200.10
ns4.saasplaza.sg. 5 A 172.188.56.149
ns4.saasplaza.us. 5 A 198.181.200.11
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0