UPC and Manufacturer's Product Code

The MPN is taken from the product code of your products.
UPC is not required.

Hi,

It's not that simple. Google does not require the UPC and the MPN.

It depends in what category you put your products and where you are based.
Here is a page which list the requirements for the USA (if you're based there):
support.google.com/merchants/bin/answer....en&answer=1344057#US
In some cases, none are required. In some cases, two of the UPC/MPN/brand are required. In some cases, only the brand is required.

In most cases with HikaShop, you simply set the MPN in the product code and set the brand in the brand field of the plugin and you're good to go.

If you really want to enter the UPC, you will have to create a custom product field to enter that value in each product and then you will have to modify the code of the plugin to include the value in the XML. It's quite, simple just add the line:
$xml.="\t".'<g:upc>'.$product->upc.'</g:upc>'."\n";
after:
$xml.="\t".'<g:condition><![CDATA[ '.$plugin->params['condition'].' ]]></g:condition>'."\n";
in the file plugins/hikashop/google_product/google_product.php
For the mpn, you can also create a custom product field and just change the line:
$xml.="\t".'<g:mpn>'.$product->product_code.'</g:mpn>'."\n";
to:
$xml.="\t".'<g:mpn>'.$product->mpn.'</g:mpn>'."\n";
to get the value from the custom field instead of the value from the product code.