Currently, when a file transfer fails for some reason, there is no indication about that error. You need to check the size of the received file to notice that it's actually 0 bytes and you have to use a terminal and --debug to find out what is going wrong. It would be nice if the ft-handler would show an error message when something goes wrong. Reproducible: Always
If I am not wrong you are wanting to have a error dialog to display the message, at line 135 filetransfer-handler.cpp , right ?
https://git.reviewboard.kde.org/r/116606/
For records keeping, we want to show up a standard system notification, handled by KNotification, not a message box. (There is Event/telepathyError which might be fitting)
Dear user, unfortunately Telepathy is no longer maintained. Please migrate to another solution, e.g. for Jabber a possibility is Kaidan, for Matrix a candidate is NeoChat.