withholding tax not calculated at the time of payment

Hello gurus

I've done all the configuration required for the extended withholding tax type-also have updated the tax type and code in the vendor master.

Now when i make the payment, the withholdign tax type is not deducted and no posting is made in the acccount assigned for the extended withholding tax ..

here are the configuration that i made:

Check Withholding tax country:

Define Withholding tax type for Payment Posting

Define Exchange Rate Type for withholding tax type

Define Withholding tax code:

Assign withholding tax types to Company Code

Activate Extended Withholding tax:

Assign Accounts for Withholding Tax to be paid over

after the above steps i updated the vendor master date with the extended withholding tax type and code

I hve NOT configured the withholding tax type for Incoming invoice ( since i'm not deducting the tax at the time of invoicing - we want it to be at the time of payment)

• this is for country key - US

Please help me . . is there any configuration step that i'm missing.

thanks in advance

Michelle