amount remaining in payment schedule not deducted by amount withheld

Hi All,

need help if someone has faced this issue before / has idea what is going on

I have standard AP invoice with withholding tax (amount withheld)

For example :

standard invoice $1000, amount withheld $200. amount remaining in payment schedule $1000 (not $800 as intended)

Treasury build payment batch, still can pay $1000, not $800

1. What cause this?

2. How to correct this? so treasury can only pay $800, not $1000

It only happens to some invoice within a supplier. Not happen to all invoices.

Thanks

Vic