Modify Free Products

add_filter('pr_shipping_dhl_label_args', 'modify_item_price', 10, 2);
function modify_item_price($args, $order_id) {
	if( isset( $args['items'] ) ) {
		foreach ($args['items'] as $item_key => $item_value) {
			if( $item_value['item_value'] == 0 ) {
				$args['items'][ $item_key ]['item_value'] = 0.01;
			}
		}
	}
	return $args;
}