How can I add the credit card fee, including the GST amount, to the total of the invoice?

Hi Andrew

All Sales forms require Items - Create a Service (or Other Charge)-type Item for this called "CC FEE" or similar. Link it to an applicable Income account (You may need to set up a new one eg CC Fees) You can select the GST tax code to ensure it calculates that also & you can choose for it to calculate the fee itself as a % or a ($) amount.

You then add this line to the invoice 😊

NOTE: If you're using a %-based Item & your invoice has multiple lines, it calculates based on the preceding line amount ONLY. Therefore, you need to add the "Subtotal" line Item first: