PHP problems with linking HTML. Doesn’t redirect

Basically my shirt e-commerce website won’t redirect to my html website. Whenever I try to click on the virtual try on button next to the shirt, it doesn’t redirect me to the page instead it just loads and refreshes the current page. Any tips?
Here is my code:

<form action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]); ?>" method="get">
    <input type="hidden" name="product_id" value="124">
    <input type="submit" value="Virtual Try ON" name="form_virtual_try_on">
</form>

<?php
$product_id = $_GET['product_id'] ?? '';

switch ($product_id) {
  case '124':
    $text = 'Virtual Try On';
    $link = 'vton_ls.html';
    break;
  default:
    $text = '';
    $link = '';
    break;
}

if (isset($_GET['form_virtual_try_on'])) {
  $product_id = $_GET['product_id'];
  if ($product_id == '124') {
    header('Location: vton_ls.html');
    exit;
  } else {
    echo "Invalid product ID";
  }
}
?>

<div class="share">
    <?php echo LANG_VALUE_58; ?> <br>
    <div class="sharethis-inline-share-buttons"></div>
</div>

I tried GET, switch case, and redoing all my codes from scratch but it doesn’t seem to work.