Thai Localization - Withholding Tax

This module lets you set up withholding tax rates and apply them to invoices and payments.

• Create withholding tax records with a name, a percentage rate, and a dedicated withholding tax account. Only accounts flagged as "WT Account" can be selected, and the module blocks saving a withholding tax that points to a normal account.
• On products, you can set a withholding tax for customer invoices and a separate one for supplier bills. When you add such a product to an invoice line, the matching withholding tax is filled in automatically on the line.
• The withholding tax column is visible on invoice lines and journal items, so you can review or change it per line.
• When you register a payment for invoices that carry withholding tax, the payment wizard shows a Withholding Tax field and a Withholding Base. The payment amount is reduced by the withholding amount, and the difference is posted to the withholding tax account.
• If invoices with withholding tax belong to several different partners, the module refuses to register a combined payment and asks you to group payments instead.

It touches accounting accounts, invoices and their lines, payments, the payment registration wizard, and products. A new "Withholding Tax" menu is added under Accounting/Invoicing.