nicolas wrote: There is no need to make an override. As the plugin is not included in HikaShop, it won't be updated automatically when you update HikaShop. And there shouldn't be any need to update it manually.
However, the override path that Jerome gave you is the correct one. That was not always possible so maye you're using an old version of the plugin which doesn't support the override ?
I guess I use the last one, I bought it 2 days ago.
But if this plugin is rarely updated I will use the original files (back them up first) to change to my liking.
P.s. About the override, I assume thats in the template folder, and then:
"html/media/com_hikashop/plugins/invoice.php"