问当表单成功时，Ajax不返回回显

EN

[code] if (response === 'Saved') {
do this}else{do that}[code]

<input type = "submit" name = "register" id = "reg_btn" >

 $('#reg_btn').on('click', function(){
    var email = $('#email').val();
    var fname = $('#fname').val();
    var lname = $('#lname').val();
    var password = $('#password').val();
    if (email_state === false || fname_state === false || lname_state === false || pword_state === false) {
      $('#error_msg').text('Fix the errors in the form first');
      return false;
    }else if (email_state === true && fname_state === true && lname_state === true && pword_state && true)
    {
      // proceed with form submission
      $.ajax({
        url: '../PHP/reg2.php',
        type: "post",
        data: {
            'save' : 1,
            'email' : email,
            'fname' : fname,
            'password' : password,
        'lname' : lname

        },
        success: function(response){


                alert(response);
            window.location = 'succesful_registration.html';
                    }

        }
      });
    }
 });

   $db = mysqli_connect ("localhost","snapitlive","2XEq6NI0QortZIdh","snapitlive");
  if($db == false)
    {
        die("ERROR: Could not connect. " . mysqli_connect_error());
    }

    $webform = (filter_Input(\INPUT_POST, 'save', FILTER_SANITIZE_SPECIAL_CHARS));
    if ($webform) {
    $first_name = filter_input(\INPUT_POST,'fname', FILTER_SANITIZE_SPECIAL_CHARS);
    $last_name = filter_input(\INPUT_POST,'lname',FILTER_SANITIZE_SPECIAL_CHARS);
    $email = filter_input(\INPUT_POST,'email',FILTER_SANITIZE_SPECIAL_CHARS);
    $mobile = filter_input(\INPUT_POST,'mobile', FILTER_SANITIZE_SPECIAL_CHARS);
    $uniqid = \uniqid();
    $password = filter_input(\INPUT_POST,'password',FILTER_SANITIZE_SPECIAL_CHARS);
    $hashpass = password_hash($password, PASSWORD_DEFAULT);
    $pw_uniqid = \uniqid();
/*$sql = "SELECT * FROM users WHERE u_ea='$email'";
    $results = mysqli_query($db, $sql);
    if (mysqli_num_rows($results) > 0) {
      echo "exists";    
      exit();
    }else{*/
            $sql = "INSERT INTO users (u_id, u_fn, u_ln, u_ea, u_mp) VALUES ('$uniqid','$first_name', '$last_name', '$email', '$mobile');";
            $sql .="INSERT INTO passwords(p_id, p_u_id, password, current) VALUES ('$pw_uniqid', '$uniqid', '$hashpass', 1);";

            $results = \mysqli_multi_query($db, $sql);
            echo 'Saved';


    exit();
    mysql_close($db);
    }