url not found after I finished Cleaning URLs with Subfolders

 <?php 

    require_once("../inc/config.php");
    require_once(ROOT_PATH . "inc/products.php");

if (isset($_GET["id"])) {
    $product_id = $_GET["id"];
    if (isset($products[$product_id])) {
        $product = $products[$product_id];
    }
}
if (!isset($product)) {
    header("Location: " . BASE_URL . "shirts/");
    exit();
}

$section = "shirts";
$pageTitle = $product["name"];
include(ROOT_PATH . "inc/header.php"); ?>

        <div class="section page">

            <div class="wrapper">

                <div class="breadcrumb"><a href="<?php echo BASE_URL; ?>shirts/">Shirts</a> &gt; <?php echo $product["name"]; ?></div>

                <div class="shirt-picture">
                    <span>
                        <img src="<?php echo BASE_URL . $product["img"]; ?>" alt="<?php echo $product["name"]; ?>">
                    </span>
                </div>

                <div class="shirt-details">

                    <h1><span class="price">$<?php echo $product["price"]; ?></span> <?php echo $product["name"]; ?></h1>

                    <form target="paypal" action="https://www.paypal.com/cgi-bin/webscr" method="post">
                        <input type="hidden" name="cmd" value="_s-xclick">
                        <input type="hidden" name="hosted_button_id" value="<?php echo $product["paypal"]; ?>">
                        <input type="hidden" name="item_name" value="<?php echo $product["name"]; ?>">
                        <table>
                        <tr>
                            <th>
                                <input type="hidden" name="on0" value="Size">
                                <label for="os0">Size</label>
                            </th>
                            <td>
                                <select name="os0" id="os0">
                                    <?php foreach($product["sizes"] as $size) { ?>
                                    <option value="<?php echo $size; ?>"><?php echo $size; ?> </option>
                                    <?php } ?>
                                </select>
                            </td>
                        </tr>
                        </table>
                        <input type="submit" value="Add to Cart" name="submit">
                    </form>

                    <p class="note-designer">* All shirts are designed by Mike the Frog.</p>

                </div>

            </div>

        </div>

<?php include(ROOT_PATH . "inc/footer.php"); ?>