Withholding Tax deduction on DownPayment

Dear All,

For Thailand country, WHT details are maintained in Vendor Master. As per requirement, WHT should not be calculated at the time of DownPayment (F-47). It should be calculated on the total amount only during Invoicing. However when I do F-47, system is calculating WHT.

Any pointers on how this can be achieved.

Best,

Rohit