Bluetooth Midi Motion turns your iOS and iPadOS devices in a wireless motion controller.
Control your iOS, iPadOS and desktop Bluetooth LE Midi DAWs , instruments and effects from your iPhone and iPad with motion.
-Up to 48 motion controllers that sends cc midi messages
-X, Y and Z axes.
-Bluetooth LE Midi.

How does it works:
Push connect button and in the opened view turn on the switch button. This will make your device discoverable by your Bluetooth MIDI host, connect it from it and you will can control your MIDI host from B.M.M.
If your MIDI host don't support Bluetooth MIDI there are some free apps on the market that creates virtual Bluetooth Midi Ports.
B.M.M. uses channel 4.

Demo video on the developer's page.