Before_add_line_item - max quantity of products in cart

[mattgeminiworktops]

I am using a before_add_line_item event to restrict the number of samples (product type) added to the cart to three.
It works to an extent as it will not add more than 3 samples to the cart, however the 'addedToCart' a toast style flash message is still displaying the success message.

I also have a max qty set on each individual product via Commerce as 1 - and this triggers a Cart Error. Ideally I would like to trigger an error when user tries to add more than three items to the cart, which displays as a toast style notification..

Any help appreciated!

{% if addedToCart %}
 <script>window.dispatchEvent(new CustomEvent("flash-msg", {detail: {msg: '{{product.title}} sample added to basket', style: 'success'}}));</script>
{% endif %}

{% if cart.errors|length %}
            <script>
             window.dispatchEvent(new CustomEvent("flash-msg", {detail: {msg: 'Max samples in basket', style: 'warning'}}));
            </script>
            {% endif %}

            Order::class,
            Order::EVENT_BEFORE_ADD_LINE_ITEM,
            function(AddLineItemEvent $event) {
                /** @var \craft\commerce\elements\Order $order */
                $order = $event->sender;

                // get the total Sample products already in the cart
                $sampleLineItems = \craft\helpers\ArrayHelper::where($order->getLineitems(), function(\craft\commerce\models\LineItem $lineItem) {
                    $purchasable = $lineItem->getPurchasable();
                    return (
                        $purchasable instanceof \craft\commerce\elements\Variant &&
                        $purchasable->getProduct()->getType()->handle === 'samples'
                    );
                });
                $totalSamples = array_sum(\craft\helpers\ArrayHelper::getColumn($sampleLineItems, 'qty'));

                if ($totalSamples + $event->lineItem->qty > 3) {
                    $event->isValid = false;
                }
            }
        );```

[nfourtythree]

Hi @mattgeminiworktops

Thank you for your question.

Adding an error to the order model should get this working for you. For example the addition of the line $order->addError('lineItems', 'You can only add 3 samples to your cart.'); under $event->isValid = false; in your code.

Thanks.