The GST check box in Provider settings needs to be ticked for GST to be an option on invoices. The reason for this is that only Providers who are registerd for GST can add it to an invoice. Those who are not registered mustn't add GST to their invoices.
To enable GST:
- Go to Provider settings
- Go to the General tab

- Tick GST Registered box

The GST box will be unticked if the Provider is not GST registered or they are not an Allied Health Provider. All Allied Health Providers will be set to true automatically - this can be turned off at any stage.
The Full breakdown is that GST will only be enabled for the following options on an invoice:
- The Fee Basis is PRIVATE
- The Claim type is MANUAL
- The Claim type is PRIVATE
- The Provider is an Allied Health Provider and the Claim type is DVA
- The Provider is GST registered and the health fund selected has GST enabled