Apex domains cannot have CNAME records.
Question and response
Question
dig ntts-idc.net.sg. NS
Answer
ntts-idc.net.sg. 3 NS ns4-09.azure-dns.info.
ntts-idc.net.sg. 3 NS ns3-09.azure-dns.org.
ntts-idc.net.sg. 3 NS ns1-09.azure-dns.com.
ntts-idc.net.sg. 3 NS ns2-09.azure-dns.net.
Authority
The response has no authority records.
Additional
ns1-09.azure-dns.com. 3 A 13.107.236.9
ns2-09.azure-dns.net. 3 A 150.171.21.9
ns3-09.azure-dns.org. 3 A 204.14.183.9
ns4-09.azure-dns.info. 3 A 208.84.5.9
ns1-09.azure-dns.com. 3 AAAA 2603:1061:0:700:0:0:0:9
ns2-09.azure-dns.net. 3 AAAA 2620:1ec:8ec:700:0:0:0:9
ns3-09.azure-dns.org. 3 AAAA 2a01:111:4000:700:0:0:0:9
ns4-09.azure-dns.info. 3 AAAA 2620:1ec:bda:700:0:0:0:9
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0