...
The Payment Terms field is populated automatically with the default terms defined for the entity for settlements with this subcontractor (for details, see Purchasing Payment Terms).
Once you replace the payment terms, the system will automatically recalculate pay dates and amounts for each payment stage (installment) if there are multiple stages in the payment process. You also can add installments and edit the installment amounts manually in the table. The sum of the installment amounts must be equal to the document total amount.
...