Apex domains cannot have CNAME records.
Question and response
Question
dig active24.com. NS
Answer
active24.com. 5 NS gama.ns.active24.sk.
active24.com. 5 NS alfa.ns.active24.cz.
active24.com. 5 NS beta.ns.active24.cz.
Authority
The response has no authority records.
Additional
alfa.ns.active24.cz. 5 A 81.95.96.2
beta.ns.active24.cz. 5 A 185.111.90.94
gama.ns.active24.sk. 5 A 185.71.158.30
alfa.ns.active24.cz. 5 AAAA 2a02:4a8:ac24:100:0:0:96:2
beta.ns.active24.cz. 5 AAAA 2a00:4b40:1000:590:185:111:90:94
gama.ns.active24.sk. 5 AAAA 2a00:1968:0:1002:185:71:158:30
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0