To enter your GST Number so that it appears on customer invoices you first need to ensure that you have New Zealand set as your Country Code. To do this please see the guide titled How to Change Country Code.
Then to update or add your GST Number click on Settings (1) in the left hand sidebar menu and then click Company Settings (2).

In the Company Settings section enter your GST Number in the GST Number field.

Scroll down to the bottom of the page and click the Save button in the lower right hand corner.

3. Your GST number will now show at the top of all customer invoices;
