If you've created invoices that do not have GST and should have, here's how to fix it:
- Go to Reports.
- In the Go to Reports field, enter Transaction List by Date.
- Select Customise.
- Select the correct date range.
- Under Rows/Columns, select Change Columns.
- Select Tax Amount.
- Select Run Report.
- Select each invoice that's missing GST, add the GST, and then select Save.