I try to send the message A 0 or A 1 to the arduino via serial object but I'm getting an error. What am I missing?

and my arduino code:

const int LED_pins[] = {11, 12, 13};
const int NUM_LEDS = 3;

void setup() {
  for (int i = 0; i < NUM_LEDS; i++) {
    pinMode(LED_pins[i], OUTPUT);
  }
  Serial.begin(115200);
}

void loop() {
  if (Serial.available() > 0) {
    char id = Serial.read();
    int state = Serial.parseInt();
    if (id == 'A') {
      digitalWrite(LED_pins[0], state);
    } else if (id == 'B') {
      digitalWrite(LED_pins[1], state);
    } else if (id == 'C') {
      digitalWrite(LED_pins[2], state);
    }
  }
}

[[list fromsymbol] expects a symbol obviously, but what is not obvious is that symbols need to be tagged explicitly as a symbol or they are simply "text"...... it drives us nuts sometimes.
So you need the message [symbol A $1(
But that will not work...... as it will only receive the A because of the space afterward...... so you will have to stick the $1 to the A....... [symbol A$1( will produce 65 48 (for 0) and 65 49 (for 1).
David.

if (id == 'A') {
      digitalWrite(LED_pins[0], state);}

to this:

if (id == 'A') {
      digitalWrite(LED_pins[0], !state);

so when I'm sending A 1 to arduino I'm turning led ON and I would like to receive in pd the message "Led1 On" in pd

const int LED_pin[] = {13, 12, 11};
const int NUM_LEDS = 1;
const char LED_ids[] = {'A', 'B', 'C'};

void setup() {
  for (int i = 0; i < NUM_LEDS; i++) {
    pinMode(LED_pin[i], OUTPUT);
  }
  Serial.begin(115200);
}

void loop() {
  if (Serial.available() > 0) {
    char id = Serial.read();
    int state = Serial.parseInt();
    for (int i = 0; i < NUM_LEDS; i++) {
      if (id == LED_ids[i]) {
        digitalWrite(LED_pin[i], !state);
        Serial.print("led");
        Serial.println(i + 1);
        Serial.print("");
        Serial.println(!state);
        break;
      }
    }
  }
}