Add or update cart quantity threw api

Hi,

I am building an api to manage my users cart

First I had to create a function to enable the cart management

private function loadCart()
    {
        WC()->frontend_includes();
        WC()->session = new WC_Session_Handler();
        WC()->session->init();
        WC()->customer = new WC_Customer( get_current_user_id(), true );
        WC()->cart = new WC_Cart();
    }

Then I have a function to add produts to the cart

    public function updateCart($request)
    {
        $this->loadCart();
        foreach ($request->get_json_params() as $item) {
            WC()->cart->add_to_cart($item['id'], $item['quantity'], $item['variationId']);
        }

        return new WP_REST_Response(WC()->cart->get_cart());
    }

This is not adding any product, WC()->cart->add_to_cart($item['id'], $item['quantity'], $item['variationId']) is returning me a cart key but the new item is not returned by WC()->cart->get_cart()

If I am running WC()->cart->empty_cart(); just before my loop, all the new items are added to the cart but the old one are removed

Thanks for the help