Apex domains cannot have CNAME records.
Question and response
Question
dig sihems-thai.dimaster.ch. NS
Answer
sihems-thai.dimaster.ch. 5 NS ns1.dimastersoftware.ch.
sihems-thai.dimaster.ch. 5 NS ns2.dimastersoftware.ch.
Authority
The response has no authority records.
Additional
ns1.dimastersoftware.ch. 2 A 157.90.88.146
ns2.dimastersoftware.ch. 2 A 185.48.231.250
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0