Hi userinfo30, 

Currently with our invoice feature an amount must be added to a transaction line before any GST can be calculated on the invoice. Are you looking for the GST to be separated on the invoice i.e it's own line item on the invoice separate from the amount of the product/service?

If you have already turned on the GST centre within your file, unfortunately this option is no longer available as the system will flag that "Make sure all your transactions have a GST rate before you save."

Let me know if you have more questions regarding this,

-Steven