Apex domains cannot have CNAME records.
Question and response
Question
dig ptasp.com. NS
Answer
ptasp.com. 4 NS ns1.ptasp.com.
ptasp.com. 4 NS ns2.ptasp.com.
ptasp.com. 4 NS ns3.ptasp.com.
Authority
The response has no authority records.
Additional
ns1.ptasp.com. 4 A 62.28.40.139
ns2.ptasp.com. 4 A 62.28.40.141
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0