Modbus Slave Not Responding to Master

// Slave doesn't register any data or mapping tables

#include <modbus/modbus.h>
#include <stdio.h>

int main() {
  int listening_socket;
  modbus_t *ctx;
  modbus_mapping_t *mb_mapping;
  
  // TCP slave on port 502
  ctx = modbus_new_tcp('0.0.0.0', 502);
  
  // Create mapping: coils, discrete inputs, holding registers, input registers
  mb_mapping = modbus_mapping_new_start_address(
    0, 100,  // Coils (0-99)
    0, 100,  // Discrete inputs (0-99)
    0, 100,  // Holding registers (0-99)
    0, 100); // Input registers (0-99)
  
  if (mb_mapping == NULL) {
    fprintf(stderr, 'Failed to allocate mapping\n');
    return -1;
  }
  
  // Set initial values
  mb_mapping->tab_registers[0] = 1234;  // Holding register 0 = 1234
  
  listening_socket = modbus_tcp_listen(ctx, 1);
  modbus_tcp_accept(ctx, &listening_socket);
  
  for (;;) {
    uint8_t query[MODBUS_TCP_MAX_ADU_LENGTH];
    int rc = modbus_receive(ctx, query);
    if (rc > 0) {
      modbus_reply(ctx, query, rc, mb_mapping);
    }
  }
}