Apex domains cannot have CNAME records.
Question and response
Question
dig tunsif.com. NS
Answer
tunsif.com. 5 NS ns-1438.awsdns-51.org.
tunsif.com. 5 NS ns-1817.awsdns-35.co.uk.
tunsif.com. 5 NS ns-1073.awsdns-06.org.
tunsif.com. 5 NS ns-1599.awsdns-07.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0