How do I get the words 'Tax Invoice' to appear on the account when I charge GST?

If you charge GST by ticking the GST box on an account's Fee page, the words 'Tax Invoice' will automatically appear above the account number on your printed account. If no GST is charged, the words 'No GST added' will appear in this position. The 'No GST added' note can be removed if you prefer by unticking the relevant box in the Options form (Misc page).

I never charge GST. How can I turn the GST functions off?

All the GST functions can be hidden by unchecking the tick box in the Options on the Miscellaneous page.