header（'Location：'。$ page）功能不起作用

Question

Can anybody help me? I perform my shop cart using php and in some moment after several customizations my header() function stopped working. I just can not figure why. I appreciate any help.

$page = 'index.php';
if (isset($_GET['add'])) {
    $con = mysqli_connect("localhost", "noivaem", "password", "noivaem") or die (mysqli_error());
    $quantity = mysqli_query($con, "SELECT id, quantity FROM Products WHERE id=".mysqli_real_escape_string($con, $_GET['add']));
    while($quantity_row = mysqli_fetch_assoc ($quantity)) {
        $_SESSION['cart_'.(int)$_GET['add']]+=1;}
    header('Location: '.$page); }

Answer 1

Check to ensure nothing is being output to the browser before header()

Hint: You have an error in your code.