Good day, jenny25.

The GST out of scope will show on the drop-down depending on the selected transaction. 

The option to add a GST is unavailable for Transfer transactions. This is only available if you select either Expense or Cheque.

Please refer to the screenshots for your reference:

You can also check out these articles to learn more about GST FAQs:

• Simpler GST FAQ

• GST Centre Update FAQs

If I can be of any additional help, please tag me directly.