Ui only mode keybinds

Been trying to set up custom keybinds for my players all day. I have it working almost perfectly except I can’t seem to bind the R button. What does the R button do when in Ui only mode? I can’t set it because something is using it.
Why is there not a list of keybinds that UI only mode uses? This is needed greatly.
What is needed even more is the ability to custom set these binds.