Apex domains cannot have CNAME records.
Question and response
Question
dig myconvento.cloud. NS
Answer
myconvento.cloud. 5 NS x.ns.joker.com.
myconvento.cloud. 5 NS y.ns.joker.com.
myconvento.cloud. 5 NS z.ns.joker.com.
Authority
The response has no authority records.
Additional
x.ns.joker.com. 5 A 194.245.103.13
y.ns.joker.com. 5 A 23.88.49.189
z.ns.joker.com. 5 A 192.95.37.184
y.ns.joker.com. 5 AAAA 2a01:4f8:c0c:165b:0:0:0:1
z.ns.joker.com. 5 AAAA 2607:5300:203:7e6d:0:0:0:2222
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0