BasicNetwork.performRequest: Unexpected response code 400

<?php

if ($_SERVER['REQUEST_METHOD']=='POST'){
    $user = $_POST['email'];
    $pass = $_POST['password'];

    $sql = "select * from users where email = '$user' AND password = '$pass'";

    require_once('config.php');
    $result = mysqli_query($con , $sql);
    $check = mysqli_fetch_array($result);

    if(isset($check)){
        echo "success";
    }else{
        echo "failure";
    }
    mysqli_close($con);
}
?>

<?php
$serverName = "localhost";
$userName = "root";
$password = "";
$dbName = "testDb"

$con = mysqli_connect($serverName , $userName , $password , $dbName) or die("connect failed");
?>

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

        editTextEmail = (EditText) findViewById(R.id.editTextEmail);
        editTextPassword = (EditText) findViewById(R.id.editTextPassword);
        buttonLogin = (Button) findViewById(R.id.buttonLogin);
        buttonLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                login();
            }
        });
    }


    @Override
    protected void onResume() {
        super.onResume();

        SharedPreferences sharedPreferences = getSharedPreferences(config.SHARED_PREF_NAME , Context.MODE_PRIVATE);
        loggedIn = sharedPreferences.getBoolean(config.LOGGEDIN_SHARED_PREF , false);
        Log.e("txt" , "text is : " + loggedIn);
        if (loggedIn){
            Intent intent = new Intent(loginActivity.this , profileActivity.class);
            startActivity(intent);
        }
    }

    private void login(){

        final String email = editTextEmail.getText().toString().trim();
        final String password = editTextPassword.getText().toString().trim();

        StringRequest stringRequest = new StringRequest(Request.Method.POST, config.LOGIN_URL, new Response.Listener<String>() {
            @Override
            public void onResponse(String response) {
                Log.i("StartActivity", response.toString());
                if(response.equalsIgnoreCase(config.LOGIN_SUCCESS)){
                    //Creating a shared preference
                    SharedPreferences sharedPreferences = loginActivity.this.getSharedPreferences(config.SHARED_PREF_NAME, Context.MODE_PRIVATE);

                    //Creating editor to store values to shared preferences
                    SharedPreferences.Editor editor = sharedPreferences.edit();

                    //Adding values to editor
                    editor.putBoolean(config.LOGGEDIN_SHARED_PREF, true);
                    editor.putString(config.EMAIL_SHARED_PREF, email);
                    //Saving values to editor
                    editor.commit();

                    //Starting profile activity
                    Intent intent = new Intent(loginActivity.this, profileActivity.class);
                    startActivity(intent);
                }else{
                    //If the server response is not success
                    //Displaying an error message on toast
                    Toast.makeText(loginActivity.this, "Invalid username or password", Toast.LENGTH_LONG).show();
                    Log.e("s" , "invalid sssssssssssssssssssssss");
                }
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {

            }
        }){
            @Override
            public Map<String, String> getParams() {
                Map<String,String> params = new HashMap<>();
                params.put(config.KEY_EMAIL, email);
                params.put(config.KEY_PASSWORD, password);
                return params;
            }
        };

        RequestQueue requestQueue = Volley.newRequestQueue(this);
        requestQueue.add(stringRequest);
    }