Probleme d'ajout de donnée dans BDD

<?php
//Affichage des erreurs PHP '(à mettre au DEBUT de ta page php ! ) 
error_reporting(E_ALL);

// Connexion à la BDD + Fichier de fonctions
 include_once('includes/connect_database.php'); 
 include_once('functions.php'); 



$sql_query = "SELECT cat_id, cat_title 
 FROM categories 
 ORDER BY cat_id ASC";
  
$stmt_category = $connect->stmt_init();
if($stmt_category->prepare($sql_query)) { 
 // Execute query
 $stmt_category->execute();
 // store result 
 $stmt_category->store_result();
 $stmt_category->bind_result($category_data['cat_id'], 
  $category_data['cat_title']
  );  
}
// marque

 $sql_query = "SELECT marque_id, marque_title 
 FROM marques 
 ORDER BY marque_id ASC";
  
$stmt_marque = $connect->stmt_init();
if($stmt_marque->prepare($sql_query)) { 
 // Execute query
 $stmt_marque->execute();
 // store result 
 $stmt_marque->store_result();
 $stmt_marque->bind_result($marque_data['marque_id'], 
  $marque_data['marque_title']
  );  
}

// get currency symbol from setting table
$sql_query = "SELECT Value 
  FROM tbl_setting 
  WHERE Variable = 'Currency'";


$stmt = $connect->stmt_init();
if($stmt->prepare($sql_query)) { 
 // Execute query
 $stmt->execute();
 // store result 
 $stmt->store_result();
 $stmt->bind_result($currency);
 $stmt->fetch();
 $stmt->close();
}
 
//$max_serve = 10;

// RECUPERATION PROPRE DES VARIABLES AVANT DE LES UTILISER
 $product_title = isset($_POST['product_title']) ? $_POST['product_title'] : NULL;
 $product_category_id = isset($_POST['category_ID']) ? $_POST['category_ID'] : NULL;
 $product_marque_id = isset($_POST['product_marque_id']) ? $_POST['product_marque_id'] : NULL;
 $product_price = isset($_POST['product_price']) ? $_POST['product_price'] : NULL ;
 $serve_for = isset($_POST['serve_for']) ? $_POST['serve_for']: NULL;
 $product_description = isset($_POST['product_description']) ? $_POST['product_description'] : NULL;
 $product_quantity = isset($_POST['product_quantity']) ? $_POST['product_quantity'] : NULL;

 // get image info
    $product_image = !empty($_FILES['product_image']['name']) ? $_FILES['product_image']['name'] : NULL;
 $image_error = !empty($_FILES['product_image']['error']) ? $_FILES['product_image']['error'] : NULL;
 $image_type = !empty($_FILES['product_image']['type']) ? $_FILES['product_image']['type'] : NULL;
 
//Traitement du submit
if(isset($_POST['btnAdd'])){
 
 // create array variable to handle error
 $error = array();
 
 if(empty($product_title)){
  $error['product_title'] = " <span class='label label-danger'>Required!</span>";
 }
  
 if(empty($product_category_id)){
  $error['product_category_id'] = " <span class='label label-danger'>Required!</span>";
 }    
  if(empty($product_marque_id)){
  $error['product_marque_id'] = " <span class='label label-danger'>Required!</span>";
 } 
 if(empty($product_price)){
  $error['product_price'] = " <span class='label label-danger'>Required!</span>";
 }else if(!is_numeric($product_price)){
  $error['product_price'] = " <span class='label label-danger'>product_price in number!</span>";
 }

 if(empty($product_quantity)){
  $error['product_quantity'] = " <span class='label label-danger'>Required!</span>";
 }else if(!is_numeric($product_quantity)){
  $error['product_quantity'] = " <span class='label label-danger'>product_quantity in number!</span>";
 }
  
 if(empty($serve_for)){
  $error['serve_for'] = " <span class='label label-danger'>Not choosen</span>";
 }   

 if(empty($product_description)){
  $error['product_description'] = " <span class='label label-danger'>Required!</span>";
 }
 
 // common image file extensions
 $allowedExts = array("gif", "jpeg", "jpg", "png");
 
 // get image file extension

 $extension = end(explode(".", $_FILES["product_image"]["name"]));
   
 if($image_error > 0){
  $error['product_image'] = " <span class='label label-danger'>Not uploaded!</span>";
 }else if(!(($image_type == "image/gif") || 
  ($image_type == "image/jpeg") || 
  ($image_type == "image/jpg") || 
  ($image_type == "image/x-png") ||
  ($image_type == "image/png") || 
  ($image_type == "image/pjpeg")) &&
  !(in_array($extension, $allowedExts))){
 
  $error['product_image'] = " <span class='label label-danger'>Image type must jpg, jpeg, gif, or png!</span>";
 }
  
 if(!empty($product_title) && !empty($product_category_id)&& !empty($product_marque_id) &&  !empty($product_price) && is_numeric($product_price) &&
  !empty($serve_for) && empty($error['product_image']) && !empty($product_description) && !empty($product_quantity) && is_numeric($product_quantity)){
  
  // create random image file name
  $string = '0123456789';
  $file = preg_replace("/\s+/", "_", $_FILES['product_image']['name']);
  $function = new functions;
  $product_image = $function->get_random_string($string, 4)."-".date("Y-m-d").".".$extension;
   
  // upload new image
  $upload = move_uploaded_file($_FILES['product_image']['tmp_name'], 'upload/images/'.$product_image);

  // insert new data to menu table
  $sql_query = "INSERT INTO products (product_title, product_category_id,product_marque_id, product_price, Serve_for, product_image, product_description, product_quantity)
    VALUES(?, ?, ?, ?, ?, ?, ?, ?)";
    
  $upload_image = 'upload/images/'.$product_image;
  $stmt = $connect->stmt_init();
  if($stmt->prepare($sql_query)) { 
   // Bind your variables to replace the ?s
   $stmt->bind_param('sssssss', 
      $product_title, 
      $product_category_id, 
      $product_marque_id,
      $product_price, 
      $serve_for, 
      $upload_image,
      $product_description,
      $product_quantity
      );
   // Execute query
   $stmt->execute();
   // store result 
   $result = $stmt->store_result();
   $stmt->close();
  }
  
  if($result){
   $error['add_menu'] = " <span class='label label-primary'>Success Added</span>";
  }else {
   $error['add_menu'] = " <span class='label label-danger'>Failed</span>";
  }
 }
  
 }
?>
<!-- Le HTML -->
<div id="content" class="container col-md-12">

 <div class="col-md-12">
 <h1>Add Menu <?php echo isset($error['add_menu']) ? $error['add_menu'] : '';?></h1>
 <hr />
 </div>

 <div class="col-md-12">
 
 <form method="post" enctype="multipart/form-data">

 <div class="col-md-9">
  <div class="col-md-12">
  <label>Menu Name :</label><?php echo isset($error['product_title']) ? $error['product_title'] : '';?>
  <input type="text" class="form-control" name="product_title"/>
  </div>
     <div class="col-md-3">
     <br>
     <label>product_price (<?php echo $currency;?>) :</label><?php echo isset($error['product_price']) ? $error['product_price']:'';?>
  <input type="text" class="form-control" name="product_price"/>
  <br/>

  <label>Stock :</label><?php echo isset($error['product_quantity']) ? $error['product_quantity']:'';?>
  <input type="text" class="form-control" name="product_quantity"/>
  <br/>
     
     <label>Status :</label><?php echo isset($error['serve_for']) ? $error['serve_for'] : '';?>
  <select name="serve_for" class="form-control">
   <option>Available</option>
   <option>Sold Out</option>
  </select>
  <br/>

     <label>Category :</label><?php echo isset($error['product_category_id']) ? $error['product_category_id'] : '';?>
  <select name="category_ID" class="form-control">
   <?php while($stmt_category->fetch()){ ?>
    <option value="<?php echo $category_data['cat_id']; ?>"><?php echo $category_data['cat_title']; ?></option>
   <?php } ?>
  </select>
    <label>Marque :</label><?php echo isset($error['product_marque_id']) ? $error['product_marque_id'] : '';?>
  <select name="product_marque_id" class="form-control">
   <?php while($stmt_marque->fetch()){ ?>
    <option value="<?php echo $marque_data['marque_id']; ?>"><?php echo $marque_data['marque_title']; ?></option>
   <?php } ?>
  </select>
  <br/>
  <label>Image :</label><?php echo isset($error['product_image']) ? $error['product_image'] : '';?>
  <input type="file" name="product_image" id="product_image"/>
  </div>

  <div class="col-md-9">
  <br>
  <label>product_description :</label><?php echo isset($error['product_description']) ? $error['product_description'] : '';?>
  <textarea name="product_description" id="product_description" class="form-control" rows="16"></textarea>
  <script type="text/javascript" src="css/js/ckeditor/ckeditor.js"></script>
  <script type="text/javascript">                        
            CKEDITOR.replace( 'product_description' );
        </script>
  </div>
 </div>
 
 <br/>
 <div class="col-md-3">
  <div class="panel panel-default">
   <div class="panel-heading">Add</div>
    <div class="panel-body">
     <input type="submit" class="btn-primary btn" value="Add" name="btnAdd" /> 
     <input type="reset" class="btn-danger btn" value="Clear"/>
    </div>
  </div>
 </div>
 </form>
 </div> 
 <div class="separator"> </div>
</div>
   

<?php 
 $stmt_category->close();
 include_once('includes/close_database.php'); ?>

if($stmt->prepare($sql_query)) { 

<?php
$upload_image = 'upload/images/'.$product_image;
try{
    // insert new data to menu table
 $sql = "INSERT INTO products (product_title, product_category_id,product_marque_id, product_price, Serve_for, product_image, product_description, product_quantity)
   VALUES(?, ?, ?, ?, ?, ?, ?, ?)";
 $a_datas = array('sssssss', 
     $product_title, 
     $product_category_id, 
     $product_marque_id,
     $product_price, 
     $serve_for, 
     $upload_image,
     $product_description,
     $product_quantity
     );   
 $stmt = $connect->stmt_init();
 $prepare = $stmt->prepare($sql_query) { 
 // Execute query
 $result = $prepare->execute($a_datas);
    $stmt->close();
}catch(Exception $e){
  echo "<br><b>Erreur !</b>";
  echo "<br><b>Requete SQL :</b> ".$sql;
  echo "<br><b>a_datas = </b><br>";
  print_r($a_datas);
}