Adding Manufacturers_id to Invoice/packing Slip

I'd like to add manufacturers id onto the invoice/packing slip to create a unique product code along with the Product table product id. I've managed to add the product id bit, but have come unstuck with the manufacturers id as this is not in the orders table. Any suggestions?

      '        <td class="dataTableContent" valign="top" align="left">' . $order->products[$i]['id'] . '</td>' . "\n" .

You will need to do a look up on the manufactuers_id as it is not stored on the Order with something like:

$chk_manufacturers_id = zen_products_lookup($order->products[$i]['id'], 'manufacturers_id');

Forgive me, but my knowledge is limited. I added the code you suggested and the following line for the input into the table on the invoice.php

            '        <td class="dataTableContent" valign="top" align="left">' . $products->manufacturers[$i]['id']. ''. "\n" .

Nothing showed up. Is the above correct?

That is because I suggest that you make a new variable:

$chk_manufacturers_id = zen_products_lookup($order->products[$i]['id'], 'manufacturers_id');

then use the variable $chk_manufacturers_id as this will have the Products manufacturers_id in it ...

I am not sure what you want to do with the manufacturers_id but it will now be in the variable:
$chk_manufacturers_id