To add non-standard GST lines
For some invoices GST is only payable on a particular portion. For example the total amount due is $1,250.17. The GST amount is $97.20.
Obtain the GST amount from the invoice and multiply it by 11 to get the amount subject to GST (eg: $97.20 x 11 = $1,069.20).
Click plus
on the lines toolbar.
Enter the line details
Set the Tax Code to TX3 and enter the total from your calculation in the Amount field. eg: $1,069.20
Subtract the total of the first line from the total bill to get balance of bill. (eg: $1,250.17 - $1069.20 = $180.97)
Click plus
on the lines toolbar.
Enter the lines details
Set the Tax Code to TX1 and enter the total from your calculation in the Amount field. eg: $180.97
Your GST should now be correct, as is the bill total.