php - Set quantity of product in WooCommerce cart programatically

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Answer

Solution:

Figured it out.

Have to edit the foreach to foreach($items as $cart_item_key => $item), and then use WC()->cart->set_quantity( $cart_item_key, 1 );.

Here's the full code:

add_action( 'woocommerce_before_calculate_totals', 'change_price_of_product' );


function change_price_of_product() {
    $items = WC()->cart->get_cart();
    $coupons = WC()->cart->applied_coupons;
    
    $only_one_gift = 0;
    
    if (in_array('getmygift', $coupons)) {
        
         foreach($items as $cart_item_key => $item) {
                if (isset($item['product_id'])) {
                    
                    if ($only_one_gift > 0) {
                        break;
                    }
                    
                    
                    if (($item['product_id']) == 5261) {
                        $only_one_gift++;
                        $item['data']->set_price( 0 );
                        WC()->cart->set_quantity( $cart_item_key, 1 );
                    }
                }
            }
    }
}

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