Apex domains cannot have CNAME records.
Question and response
Question
dig smartspb.net. NS
Answer
smartspb.net. 5 NS ns2.smartspb.net.
smartspb.net. 5 NS ns4.smartspb.net.
Authority
The response has no authority records.
Additional
ns2.smartspb.net. 5 A 62.152.37.186
ns4.smartspb.net. 5 A 217.119.16.90
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0