Button Viewer
Some keys may have obscure names. Depending on your keyboard layout, Reemap might even show the wrong key names.
You can see what Reemap thinks a key or mouse button is called with the Button Viewer tool.
Click on Tools > Button Viewer.

This window will appear:

To use this tool, Reemap must be out of focus. Otherwise, keyboard inputs will not show up.
When you press a button, Reemap will display what it thinks that button is called.
Reemap