Hi there Aki
It may be because of the way you have pasted your code that it has a mistake in teh postion of the : in the first line of code. It is better to post it between two lines of three ```
live_loop :arp do
midi (octs :e1, 3).tick, sustain: 0.1
The code above DOES send midi output on my Sonic Pi which I am receiving in the free VMPK synth via a virtual midi port “iac driver sonic” which I have set up on my Mac. It will use every midi channel and every connected midi port. If you look at the IO preference panel in the Sonic Pi Prefs you will see a list of these. You can use port: if you want to restrict it to just one port.
Finally you should see the outgoing midi in the log window, unless you have turned off midi logging.
I suspect that your problem may be in routing the midi from Sonic Pi to ProTools. I haven’t used this (I use Ableton Live and Logic Pro). Also you don’t say what platform you are running Sonic Pi on. (Windows or Mac). You may find that the ProTools manuals gives you help in making the connection.