Hi there Kiwi,
Welcome to the Community, I'd be happy to help with your questions about invoicing
.
In order to add GST to the invoice, you'll first need to set it up in the Sales Tax Center listed under Taxes from the left menu. The following article includes steps on how to add and edit tax rates: https://community.intuit.com/articles/1145271 .
Once set up, you'll have the option to select the tax if it applies to that particular transaction. The screenshot below will show you where it's located on the invoice.
I'll be here to assist if you have any further questions. Thanks
