How do I fix a 500 internal server erro such as this

I already gave it permssion in my server but still giving me this error.

here's the code

require_once 'core.php';

$valid['success'] = array('success' => false, 'messages' => array());

if($_POST) {

$productName = $_POST['productName']; $productImage = $_POST['productImage']; $quantity = $_POST['quantity']; $rate = $_POST['rate']; $brandName = $_POST['brandName']; $categoryName = $_POST['categoryName']; $productStatus = $_POST['productStatus'];

$type = explode('.', $_FILES['productImage']['name']); $type = $type[count($type)-1]; $url = '../assests/images/stock/'.uniqid(rand()).'.'.$type; if(in_array($type, array('gif', 'jpg', 'jpeg', 'png', 'JPG', 'GIF', 'JPEG', 'PNG'))) { if(is_uploaded_file($_FILES['productImage']['tmp_name'])) { if(move_uploaded_file($_FILES['productImage']['tmp_name'], $url)) { $sql = "INSERT INTO product (product_name, product_image, brand_id, categories_id, quantity, rate, active, status) VALUES ('$productName', '$url', '$brandName', '$categoryName', '$quantity', '$rate', '$productStatus', 1)";

if($connect->query($sql) === TRUE) { $valid['success'] = true; $valid['messages'] = "Successfully Added"; } else { $valid['success'] = false; $valid['messages'] = "Error while adding the members"; }

} else { return false; } // /else } // if } // if in_array

$connect->close();

echo json_encode($valid); } // /if $_POST

here's the error im getting