Marco, thanks for writing. First, have you succeeded in getting the Altura to communicate with Ableton at all? You should be able to easily play some patch or synth or SOMETHING: notes with right hand and, for example, modulation with left (Function = 2).
If no, then make sure Ableton is listening on the same channel on which the Altura is transmitting. Set the transmit channel with Function = 7.
Once you establish communication, you need to MAP one of the Altura’s left-side functions to have the desired effect in Ableton. You need to sacrifice one of Modulation, Note On Velocity, or Channel Volume (Functions 2-3-4). Pick one, then follow the guidance in this Ableton article, Creating MIDI Mappings, to map the Altura to your VST.
Please let us know how this goes!