well my understanding is still the same as it was here:
giuliomoro I know nothing about it, but I would guess that serialoscd is a bridge between OSC and the monome: my guess is that it receives OSC messages from the user application and passes them over to the monome over serial, and also receives serial from the monome and passes it on as OSC to the user application. So, I guess it has to stay open throughout for the program to work!
I guess you now need to send OSC to serialoscd and receive OSC from it, using the OscSender and OscReceiver classes . This can be done using the Communication/OSC example as a starting point. That example relies on bi-directional communication with a node server, but ultimately you only need to send and receive (without the more complex handshake logic implemented in there).
As to WHAT messages to send/receive, I have no idea, that would be in the monome documentation, I imagine? As to WHERE to send the messages (what port), that's hopefully in the serialosc documentation. Note that there will be nothing here that is Bela-specific, so you can probably find better support in specialised Monome forums.
One thing that emerges from the README of serialosc is that you need to plugin the monome for the process to daemonise and do something useful. This may mean that in /lib/systemd/system/serialoscd.service it should be Type=forking as it was originally, instead of Type=simple as I changed it. I cannot test this because I don't have a monome, but you can. Make sure you look at the output of journalctl -f -n 50 -u serialoscd to see if anything useful is printed when the Monome is connected.