sales_helper.php

function add_new_sales_item_post($item, $rel_id, $rel_type)
{
    $custom_fields = false;

    if (isset($item['custom_fields'])) {
        $custom_fields = $item['custom_fields'];
    }

    $CI = &get_instance();

    $CI->db->insert(db_prefix() . 'itemable', [
                    'description'      => $item['description'],
                    'long_description' => nl2br($item['long_description']),
                    'qty'              => $item['qty'],
                    'rate'             => number_format($item['rate'], get_rate_decimals_place(), '.', ''),
                    'rel_id'           => $rel_id,
                    'rel_type'         => $rel_type,
                    'item_order'       => $item['order'],
                    'unit'             => $item['unit'],
                ]);

    $id = $CI->db->insert_id();

    if ($custom_fields !== false) {
        handle_custom_fields_post($id, $custom_fields);
    }

    return $id;
}