Cart is empty but the basket has item added

              <div id="basket-overview" class="navbar-collapse collapse d-none d-lg-block">
  <a href="basket.php" class="btn btn-primary navbar-btn">
    class="fa fa-shopping-cart">
    <?php echo isset($_SESSION['cart']) ? '<span id="cart-count">' . count($_SESSION['cart']) . '</span>' : ''; ?>
  </a>
</div>

<div id="basket" class="col-lg-9">
              <div class="box">
                <form method="post" action="add_to_cart.php">
                  <h1>Shopping cart</h1>
                  <p class="text-muted">You currently have <span id="cart-count"><?php echo isset($_SESSION['cart']) ? '<span id="cart-count">' . count($_SESSION['cart']) . '</span>' : ''; ?>

                  <p id="cart-message" class="text-success" style="display: none;"></p>
                  <div class="table-responsive">
                    <table class="table">
                      <thead>
                        <tr>
                          <th colspan="2">Product</th>
                          <th>Quantity</th>
                          <th>Unit price</th>
                          <th>Discount</th>
                          <th colspan="2"><span id="total-amount">Total</span></th>

                        </tr>
                      </thead>
                      <tbody id="cart-items">
                        <tr>
                          <td><a href="#"><img src="img/detailsquare.jpg" alt="White Blouse Armani"></a></td>
                          <td><a href="#">White Blouse Armani</a></td>
                          <td>
                <div class="input-group">
                
                <button class="btn btn-default btn-minus" type="button">-</button>
                
                <input type="number" name="product1" value="0" min="1" class="form-control product-quantity" data-product-id="1">
              
              <button class="btn btn-default btn-plus" type="button">+</button>
            
          </div>

function addToCart(productId, quantity) {
  var cart = getCart();
  if (cart.hasOwnProperty(productId)) {
    var newQuantity = parseInt(quantity);
    if (newQuantity <= 0) {
      delete cart[productId];
    } else {
      cart[productId] = newQuantity;
    }
  } else {
    cart[productId] = parseInt(quantity);
  }
  saveCart(cart);
  updateCartCount();
  calculate_total();

  // Display message
  var productName = $('#product-name-' + productId).text();
  $('#cart-message').text(quantity + 'x ' + productName + ' added to cart').show();
  
  setTimeout(function() {
    $('#cart-message').fadeOut('slow');
  }, 3000);
}

function calculate_total() {
  var cart = getCart();
  var total = 0;
  for (var productId in cart) {
    var product = getProductId(productId);
    var price = parseFloat(product.price);
    var quantity = parseInt(cart[productId]);

    // Send request to server to get discount for the product
    $.ajax({
      url: 'get_product_details.php',
      data: {productId: productId},
      dataType: 'json',
      success: function(data) {
        // Update HTML elements with discount and amount
        var discount = parseFloat(data.discount);
        var amount = price * quantity * (1 - discount);
        $('#discount-' + productId).text((discount * 100).toFixed(0) + '%');
        $('#amount-' + productId).text('$' + amount.toFixed(0));
      },
      error: function(xhr, textStatus, errorThrown) {
        console.log('Error getting product details: ' + errorThrown);
      }
    });

<?php
// Start the session
session_start();

echo count($_SESSION['cart']);
// Check if the cart is not empty
if (!empty($_SESSION['cart'])) {
    // Establish database connection.
    $conn = mysqli_connect('localhost', 'root', '', 'ecommerce_store');
    if (!$conn) {
        die('Could not connect to database: ' . mysqli_connect_error());
    }

    // Query the database to get the products in the cart
    $cart_items = array();
    foreach ($_SESSION['cart'] as $product_id => $quantity) {
        $sql = "SELECT * FROM products WHERE productID = '$product_id'";
        $result = mysqli_query($conn, $sql);
        if (!$result) {
            die('Error getting product details: ' . mysqli_error($conn));
        }
        $product = mysqli_fetch_assoc($result);
        $product['quantity'] = $quantity;
        $cart_items[] = $product;
    }

    // Close the database connection
    mysqli_close($conn);
}
?>
<!DOCTYPE html>
<html>
<head>
    <title>Shopping Cart</title>
    <link href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css" rel="stylesheet">
</head>
<body>
<div class="container">
    <h1>Shopping Cart</h1>
    <?php if (!empty($cart_items)): ?>
        <table class="table">
            <thead>
                <tr>
                    <th>Image</th>
                    <th>Product Name</th>
                    <th>Unit Price</th>
                    <th>Quantity</th>
                    <th>Discount</th>
                    <th>Amount</th>
                </tr>
            </thead>
            <tbody>
                <?php foreach ($cart_items as $cart_item): ?>
                <tr>
                    <td><img src="<?php echo $cart_item['image']; ?>" alt="<?php echo $cart_item['product_name']; ?>"></td>
                    <td><?php echo $cart_item['product_name']; ?></td>
                    <td>$<?php echo $cart_item['unit_price']; ?></td>
                    <td><?php echo $cart_item['quantity']; ?></td>
                    <td><?php echo $cart_item['discount']; ?></td>
                    <td>$<?php echo ($cart_item['unit_price'] * $cart_item['quantity'] * (1 - $cart_item['discount'])); ?></td>
                </tr>
                <?php endforeach; ?>
            </tbody>
        </table>
    <?php else: ?>
        <p>Your cart is empty.</p>
    <?php endif; ?>
</div>
</body>
</html>