Apex domains cannot have CNAME records.
Question and response
Question
dig ati.tn. NS
Answer
ati.tn. 4 NS ns4.ati.tn.
ati.tn. 4 NS ns6.ati.tn.
Authority
The response has no authority records.
Additional
ns4.ati.tn. 4 A 41.228.62.61
ns6.ati.tn. 4 A 41.228.63.61
ns4.ati.tn. 4 AAAA 2c0f:fab0:ffff:4:41:228:62:61
ns6.ati.tn. 4 AAAA 2c0f:fab0:ffff:5:41:228:63:61
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0