Why doesn't adding to the database work?

Question

PHP

Tell me why when using the code below, the addition does not work, but simply remains unchanged? php version 7.4

$title = $_POST['title'];
$get_id = $_GET['id'];

if(isset($_POST['add'])){
  $sql = ("INSERT INTO xf_category (title) VALUES (?)");
  $query = $pdo->prepare($sql);
  $query->execute([$title]);
  if($query){
    header("Location: ". $_SERVER['HTTP_REFERER']);
  }
}