I've got the steps you'll need on how to remove GST from your invoice, Tkornaat.

Please follow these steps:

1. Go to the Gear icon and select Custom form styles.
2. Select the Invoice template.
3. Go to the Content tab.
4. From the body of the invoice template, click on the pencil icon.
5. Uncheck the Tax box.
6. From the footer of the invoice, click on the pencil icon.
7. Uncheck the BAS summary box.
8. Select Done.

The following steps will help you remove the GST from your invoice, though these will not remove the GST total.

Keep me posted if you have anything else to add to customise your invoice. I'm here to help.