Callback from BTLE cannot working properly

MainActivity.java

public class MainActivity extends AppCompatActivity {
    private Button scan;
    private BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
    private BluetoothLeScanner bluetoothLeScanner = bluetoothAdapter.getBluetoothLeScanner();
    private boolean scanning=false;
    private Handler handler = new Handler();
    private static final long SCAN_PERIOD = 10000;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        scan = findViewById(R.id.scan);

        final Handler handler = new Handler();
        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                state();
                Log.d("Logger", "State Check");
                handler.postDelayed(this, 1000);
            }
        }, SCAN_PERIOD);

        scan.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if(scanning){
                    scan.setText("TURN ON");
                    scanning = false;
                }else{
                    scan.setText("TURN OFF");
                    scanning = true;
                }
            }
        });
    }

    private void state(){
        if(scanning){
            if(bluetoothAdapter!=null){
                if (!bluetoothAdapter.isEnabled()) {
                    Intent eintent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
                    startActivityForResult(eintent, 1);
                }else{
                    Log.d("Logger", "state: berhasil akses");
                    bluetoothLeScanner.startScan(leScanCallback);
                }
            }
        }else{
        bluetoothLeScanner.stopScan(leScanCallback);
        }
    }

    private ScanCallback leScanCallback =
            new ScanCallback() {
                @Override
                public void onScanResult(int callbackType, ScanResult result) {
                    super.onScanResult(callbackType, result);
                    Log.d("Logger", "onScanResult: Berhasil Akses");
                    BluetoothDevice newDevice = result.getDevice();
                    String device_address = newDevice.getAddress();
                    Toast.makeText(MainActivity.this,"Device "+device_address+" "+String.valueOf(result.getRssi()),Toast.LENGTH_SHORT).show();
                }
            };
}

This my manifest, i declared the uses-permission. Manifest

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.androidble">

    <uses-permission android:name="android.permission.BLUETOOTH_SCAN" />
    <uses-permission android:name="android.permission.BLUETOOTH" />
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
    <uses-permission android:name="android.permission.BLUETOOTH_CONNECT" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.AndroidBLE">
        <activity
            android:name=".MainActivity"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

I want to scan BLE using bluetoothLeScanner but my program not working properly. After I debug, it is known that the callback from BTLE cannot be called. Why does this happen and what is the solution? Thank you.

FYI, i am using android 6 API.