Kontrol S MK3 keyboards & Reaper

Quote Matthew_NI :

Make sure that the Hardware Connection Service is running and that the Kontrol MK3 can see it. Note that the hardware connection service should be started automatically when you open Komplete Kontrol software for example.

You can verify that the Kontrol Mk3 is connected to the HCS by going to Settings > general > agent version on the device, it should say version 1.9.4 (or higher ?) . If it doesn't, try a different USB-C cable,and/or a USB-C hub instead of connecting directly.

How to set up your Kontrol S-Series MK3

Also check that the keyboard is set to Midi 1.0 : How to Switch a Kontrol S-Series MK3 Keyboard to MIDI 1.0

You can check on your keyboard, press SETTINGS MIDI, Hardware, navigate until MIDI Version selection, make sure it is set to MIDI 1.0. Reboot the keyboard if needed.

You also should see a prompt to do the following:

This how to proceed: My USB MIDI Device isn't working on my Mac