If I open the example SuperCollider/Communication/remote-control on the Bela IDE and run it, then copy the content of the file remote.scd and paste it in the SC IDE, I then execute this in three different blocks:
( // connect to the already-running remote belaserver
Server.default = s = Server("belaServer", NetAddr("bela.local", 57110));
s.options.maxLogins = 4; // should match the settings on the Bela
s.initTree;
s.startAliveThread;
);
then
// Communicate with the server
s.plotTree; // show all active nodes
s.freeAll; // free all nodes
(
SynthDef('karp', {arg freq=200, amp=0.5, pan=0, dur=1, trig=1, delaytime=2, decaytime=2, coef=0.1;
var sig, env;
coef.poll(2);
sig = Pluck.ar(WhiteNoise.ar(1), trig, delaytime, freq.reciprocal, decaytime, coef);
env = EnvGen.ar(Env.perc(0.01, dur), trig, doneAction: 2);
Out.ar(0, Pan2.ar(sig * env * amp, pan));
}).add;
);
Ndef('mix', {
var sig = In.ar(50, 2);
Out.ar(0, FreeVerb.ar(sig));
}).play;
Then this produces a sound:
Synth('karp', ['dur', 2, 'freq', 62.midicps, 'amp', 1.0, 'decaytime', 0.5, 'coef', 0.1]);
If things don't work, make sure you use the same value for the first argument of NetAddr as you are using to connect to the board via the browser. Depending on your system, one or more of 192.168.7.2, 192.168.6.2 and bela.local will work. If you have a VPN, try disabling that.