Esp32 modbus tcp slave

#include <Modbus.h>
#include <WiFi.h>

#define BUFFER_SIZE 128

// Modbus TCP object
Modbus modbus;

// TCP/IP interface object
WiFiServer server(502);

// Modbus slave ID
const int SLAVE_ID = 1;

// Modbus function codes
const int FC_READ_COILS = 0x01;
const int FC_READ_INPUT_REGISTERS = 0x03;
const int FC_WRITE_MULTIPLE_COILS = 0x0F;
const int FC_WRITE_MULTIPLE_REGISTERS = 0x10;

// Modbus status codes
const int STATUS_OK = 0x00;
const int STATUS_ILLEGAL_FUNCTION = 0x01;
const int STATUS_ILLEGAL_DATA_ADDRESS = 0x02;
const int STATUS_ILLEGAL_DATA_VALUE = 0x03;
const int STATUS_SLAVE_DEVICE_FAILURE = 0x