Plug the Pi into the MixPre's USB‑A port and give it ~30 seconds to boot.
Pair this phone once: on the Pi's page open Settings → Pair a phone, then scan or paste the link.
Keyboard mode: no faders, and lights are a guess.
Moves through the MixPre's menus, like its own knob.
This input has no fader or knob on the controller. Use the buttons.