In the Supplier Payments screen when paying an account you can now tag invoices that you want to pay first, which will add to the "Left to Post" field and then enter that amount in the "Amount" field, press the "tab" key and click on Process or F12. This is handy if you don't know the amount you are going to pay, only the invoices. You can also enter the amount first, as normal, then click on Auto Post or double click on the invoices you are paying and then Process.