When you enter receipts, you should first select a vendor. All outstanding invoices, credit notes and advances appear in the list at the bottom right, now you should all documents in the top list (either by double clicking or by "Add"), which should be offset by the receipt of payment.
If an incorrect document was clicked, it can be a double click or "Remove" transported back to the lower list.
The payment amount is then calculated from all the evidence. Check the amount and add the account and the text. If a cash discount deduction was made, add the line discount (or residual) with amount and account. Confirm with "Save".
Payment can only be saved if all the documents are cleared!!
As long as the payment is not definitely (transfer to GL) was recorded, it can be edited.
Partial payments are described in the Register bills.
If you have entered under Tools / Options / Vendors / payment account to a standard account, you can use the "Payment" Enter invoice, which you want to pay with a date and press "Payment".