If you haven’t bought the “Invoicing with InvoiceXpress for WooCommerce” plugin yet, you can do it here.
After downloading the plugin zip file from your account on our plugin store, you should upload it to your WordPress install on Plugins > Add new > Upload Plugin, and then activate it.
If you already have the free version, make sure to deactivate it first.
You should now set up the InvoiceXpress and WooCommerce taxes.