f.myconvento.com has no CNAME records.
Question and response
Question
dig f.myconvento.com. NS
Answer
The response has no answer records.
Authority
myconvento.com. 183 SOA x.ns.joker.com. hostmaster.joker.com. 2025121049 14400 3600 1209600 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0