I've menaged to downgrade the keyboard firmware, but it still doesn't work.
Prior to the downgrade the XIM4 was blinking yellow light when I plugged the dongle.
After the downgrade it shows a pulsing red light as it should, but still no sign of it reacting to any keystroke. I paired the XIM4 to the manager app thing and it shows it recognizes both mouse and keyboard, but then I try to input something to a profile and nothing happens. I'm guessing it works only with Apex. Hopefully I'll manage to grab one, at least to test this.