The reason it is only working in your focused window is that you've not setup any way of broadcasting it to your other clients.

All you need for that is a mapped key. Here is the official Wiki page: http://isboxer.com/wiki/Mapped_Key

And here is a video tutorial on them: https://www.youtube.com/watch?v=8lzHM_SmFvk This tutorial is for a slightly older version of ISBoxer, but the processes are more or less the same. ISB42 just uses a slightly different keymap layout. In general you can create your mapped keys in one of the key maps ending in "Hotkeys". For example ISBoxer 42 Custom Hotkeys should work fine for most teams setup through the quick setup wizard.