I proferred a tutorial on this (regarding firewall). GUFW (Gnome Uncomplicated FireWall) has rules you can add, including one for KDE connect to be allowed through, but as Aravisian has said, we need more information. Have had issues in Antix, but resolved by installing GUFW and adding the rule.
Whilst this was aimed at issues facing users with Zorin Connect, it should also assist users of KDE connect.