If you need to pay the invoice, you need to select it and then choose the option payment, there you can pay it.
If you take off the invoices you need to Delete the invoice, that would be the only option, since the program is going to keep the order or the invoices, there is no option to remove certain invoices and then turn it back into the list.
To get more help you can also summit the request here https://www.nch.com.au/support/