KC868-A4 Bluetooth momentary Switch

[franco.demei@gmail.com]

I'm trying to program four momentary switch via bluetooth commands. I don't understand why I can't enable  "Relay3".
To compile KC868-A4 code I'm using "Arduino IDE". To program Android code  "MIT App Inventory" .
 Here is the codes I Used.  Can some one help me to understand where is a mistake ? Tank You.

AI Code     

Arduino IDE Code:

#include "BluetoothSerial.h"
BluetoothSerial SerialBT; // RX | TX
int Relay1 = 2;
int Relay2 = 5;
int Relay3 = 15;
int Relay4 = 4;
void setup() {
  pinMode(Relay1, OUTPUT);
  pinMode(Relay2, OUTPUT);
  pinMode(Relay3, OUTPUT);
  pinMode(Relay4, OUTPUT);
 
  Serial.begin(19200);   // Serial monitor
  SerialBT.begin(19200); // Bluetooth serial communication
 
  Serial.println("Bluetooth Control for KC868-A4 Relays");
}
void loop() {
  if (SerialBT.available()) {
    char command = SerialBT.read();
   
    // Command format: '1' to '4' for relays 1 to 4
    if (command >= '1' && command <= '4') {
      int relay = command - '1' + 2; // Calculate the relay control pin
         
      digitalWrite(relay, !digitalRead(relay));
   
      Serial.print("Relay ");
      Serial.print(command);
      Serial.print(" is ");
      Serial.println(digitalRead(relay) ? "ON" : "OFF");
    }
  }
}