It depends. Basically there are two tables in the Payment Entry screen: (i) SI or PI allocation table & (ii) Deduction or Loss. The total of both this table should be equal to the amount mentioned in the ‘Pay’ section.
So, if your allocation is less than Pay amount, you would have +ve amount in deduction. Example could be exchange gain or loss. And example of -ve amount could be discount received.
Hope this helps.
_Liyakat