In the app "Import Supplier Invoices (ID F3041)" in the template the fields related to withholding tax are not available for input. Is it something i'm not aware of or there is no withholding tax fields at all in the template?
Please check the SAP Help Portal page Import Supplier Invoices where you can find all the default and available fields of the template of Import Supplier Invoices.
As you see there is no field for Withholding tax.
The reason is, that for Import Supplier Invoices app, there is no need to input the Withholding tax. The logic would derive the Withholding tax customizing from the vendor automatically.