Add GTIN field in Woocommerce pdf invoices packing slips

Hi,

First of all thanks for your great free plugin.

I’m trying to add the GTIN field (I’m using it for HS CODE) in PDF invoice.
For this, I’m using this plugin : Woocommerce pdf invoices packing slips

Here the documentation :

https://docs.wpovernight.com/woocommerce-pdf-invoices-packing-slips/displaying-a-custom-field/#in-a-custom-template

Can you help me for the name of your field, and how to integrate it ?

Thanks a lot.
Mathieu