Custom Field from b2bking does not work

Hello, I have a custom field coming from b2bking plugin – currently the field is used for registration for specific user role.
My custom field name is b2bking_custom_field_12383

My code is this below, but it doesn’t work. It only adds the field name, but not populating the custom field:

add_action( 'wpo_wcpdf_after_order_data', 'wpo_wcpdf_delivery_date', 10, 2 );
function wpo_wcpdf_delivery_date ($template_type, $order) {
    if ($template_type == 'packing-slip') {
        $document = wcpdf_get_document( $template_type, $order );
        ?>      
        <tr class="Jastip">
            <th>Jastip Name:</th>
			<td><?php $document->custom_field('b2bking_custom_field_12383'); ?></td>
        </tr>
        <?php
    }
}