The amount of the WH Tax Amount field is based on the Tax Amountset on the Withholding Tax tab of the Sales Transaction (ie. Invoice). The Taxamount is practically the Base Amount of the Sales multiplied to the Tax Rateof the WH Tax Code.
To modify the amount on the said field:
1. Unapply Customer Payment
a. Edit the Customer Payment
b. Unmark the Apply boxunder the Apply tab > Invoices subtab
2. Edit the Invoice. Note that the Tax Amount on the Invoice form> Items tab > Withholding Tax subtab is alsoineditable. Select the tax code with a tax rate that results in the correctwithholding tax amount.
3. Re-apply Customer Payment
a. Edit the CustomerPayment
b. Mark the Apply boxunder the Apply tab > Invoices subtab