Tableau multi-dimensionnel et requête PHP

Pas forcement avec des virgules,

<div class="card">
        <div class="card-body" id="order">
            <div class="col-sm-12">
                <div class="row">

                    <!-- Je recupère mes produits présent en BDD et je boucle pour les rendre à la vue-->
                    <?php foreach ($products_list as $product): ?>


                        <div class="card" style="width: 18rem; margin-top: 25px; margin-right: 25px">
                            <img src="..." class="card-img-top" alt="...">
                            <div class="card-body">
                                <form method="post" >
                                    <h5 class="card-title"><?= $product->nom ?></h5>
                                    <input name="product_id" value="<?= $product->id; ?>" hidden>
                                    <input class="form-control" name="qt" style=" width: auto; margin-bottom: 10px" type="number" placeholder="quantité :">
                                    <button type="submit" class="btn btn-info" name="product_add_<?= $product->id; ?>"><i class="fas fa-shopping-cart"></i> Ajouter au panier</button>
                                </form>

                            </div>
                        </div>
                    <?php endforeach; ?>
                </div>
            </div>
        </div>
    </div>

    <div class="col-lg-12 col-md-12 col-sm-12">
            <div class="card mb-3">
                <div class="card-body">
                    <div class="card-title">
                        <div class="border-bottom pt-3 pb-2 mb-3">
                            <h1 class="h2 d-inline">Votre panier</h1>
                        </div>
                    </div>
                    <div class="table-responsive-md">
                        <table class="table table-striped table-bordered table-hover">
                            <thead class="thead-dark">

                            <tr>
                                <th class="w-25">Produit</th>
                                <th class="w-25">Quantité </th>
                                <th class="w-25">Action</th>
                            </tr>
                            </thead>
                            <tbody>
                            <?php foreach ($panier as $k => $v):
                                $produit = $productModel->read($k);

                            ?>

                            <tr>
                                <th><?= $produit->nom; ?></th>
                                <th><?= $v["product_qt"]; ?></th>
                                <th></th>
                            </tr>



                            </tbody>
                            <?php endforeach; ?>
                        </table>

                    </div>
                </div>
            </div>

$panier = unserialize($ordersModel->getUserPanier($user->id)->products);

$products_list = $productModel->findAll();

if(isset($_POST) && !empty($_POST)){

    $tab = [$_POST["product_id"]."a" => ["qt" => $_POST["qt"]]];

    if(array_key_exists($_POST["product_id"]."a", $panier)){
        echo "OUI";
      
    }else{
        echo "NON";
     
    }

    $tab2 = array_merge($panier, $tab);

}

$panier = ( $ordersModel->getUserPanier($user->id) && $ordersModel->getUserPanier($user->id)->products ) ? unserialize($ordersModel->getUserPanier($user->id)->products) : array();


$products_list = $productModel->findAll();

if(isset($_POST) && !empty($_POST)){

    $tab = [$_POST["product_id"]."a" => ["qt" => $_POST["qt"]]];

    $post = $_POST;
    if(existPanier($post, $panier)){
        $index = $_POST["product_id"]."a";
        unset($panier[$index]);
        $tab2 = array_merge($panier, $tab);

    }else{
        $tab2 = array_merge($panier, $tab);



    }


}

function existPanier($post, $panier) {

    if(array_key_exists($post["product_id"]."a1", $panier)){
        return true;
    }else{
        return false;
    }
    return false;
}