Hello Elving,

I will probably dissapoint you, but these forums are not ment for explaining PHP coding or Joomla coding.
I can only point you to what I wrote above, which is that the neccessary changes need to be done within the invoicehtml.php file.
If you need a custom adjustment and do not have sufficient knowledge how to do that, you can always get a paid Joomla support from us:
www.artio.net/e-shop/support-services/joomla-related-support-1h