Arduino serial monitor " -1"

Hey, im new to arduino and programming in general , im developing a project for school that consists in a arduino car controled by a android app , i already developed the app and im able to connect to the HC-06 bridge but when i click on the controls of the app nothing happens and in the serial monitor it shows "-1" when i click on the buttons . I don`t know what that means or where the problem comes from the app or the circuit .

Circuit : Im using the l298n motor bridge , Hc-06 bridge and arduino Uno

If someone can help me solve this , i would apreciate it

The arduino code is the following :

int Motor_A_Enable = 9;
int Motor_A_Reverse = 3;
int Motor_A_Forward = 4;

int Motor_B_Enable = 10;
int Motor_B_Reverse = 12;
int Motor_B_Forward = 7;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  
  pinMode(Motor_A_Enable, OUTPUT);
  pinMode(Motor_A_Forward, OUTPUT);
  pinMode(Motor_A_Reverse, OUTPUT);

  pinMode(Motor_B_Enable, OUTPUT);
  pinMode(Motor_B_Forward, OUTPUT);
  pinMode(Motor_B_Reverse, OUTPUT);
}

void loop() {

  if(Serial.available() > 0)
  {
    char data;
    data = Serial.read();
    Serial.print(Serial.read());

    switch (data)
    {
      case '1': //FORWARD
        analogWrite(Motor_B_Enable, 100);
        analogWrite(Motor_A_Enable, 100);
        digitalWrite(Motor_A_Reverse, LOW);
        digitalWrite(Motor_B_Reverse, LOW);
        digitalWrite(Motor_A_Forward, HIGH);
        digitalWrite(Motor_B_Forward, HIGH);
        break;
      case '2': //REVERSE
        analogWrite(Motor_B_Enable, 100);
        analogWrite(Motor_A_Enable, 100);
        digitalWrite(Motor_A_Forward, LOW);
        digitalWrite(Motor_B_Forward, LOW);
        digitalWrite(Motor_A_Reverse, HIGH);
        digitalWrite(Motor_B_Reverse, HIGH);
        break;
      case '3': //FORWARD LEFT
        analogWrite(Motor_A_Enable, 100);
        analogWrite(Motor_B_Enable, 0);
        digitalWrite(Motor_A_Reverse, LOW);
        digitalWrite(Motor_A_Forward, HIGH);
        break;
      case '4': //FORWARD RIGHT
        analogWrite(Motor_B_Enable, 100);
        analogWrite(Motor_A_Enable, 0);
        digitalWrite(Motor_B_Reverse, LOW);
        digitalWrite(Motor_B_Forward, HIGH);
        break;
      case '5': //REVERSE LEFT
        analogWrite(Motor_A_Enable, 100);
        analogWrite(Motor_B_Enable, 0);
        digitalWrite(Motor_A_Reverse, HIGH);
        digitalWrite(Motor_A_Forward, LOW);
        break;
      case '6': //REVERSE RIGHT
        analogWrite(Motor_B_Enable, 100);
        analogWrite(Motor_A_Enable, 0);
        digitalWrite(Motor_B_Reverse, HIGH);
        digitalWrite(Motor_B_Forward, LOW);
        break;
      default: //If bluetooth module receives any value not listed above, both motors turn off
        analogWrite(Motor_A_Enable, 0);
        analogWrite(Motor_B_Enable, 0);
    }
  }
}

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