Align CreditNote with Invoice document around withholding tax information

Please see:

https://lists.oasis-open.org/archives/ubl/201505/msg00009.html

Roberto Cisternino wrote:

Good day UBL..lers,
Unfortunately I noted there is a missing ABIE in the UBL-CreditNote-2.1 which is the WithholdingTaxTotal (actually is my fault...)
In fact if a company/freelancer is subject to the withholding tax on the invoice document it is required to apply the same tax on the credit note.
Practically the withholding tax amount is corrected by the credit note just like other amounts.

Of course the process of obtaining back the overpaid withholding tax from the tax authority is outside the invoicing process.

Another important point is that the Withholding tax (W/T) is not a VAT tax but instead an Income tax.
The AccountingCustomerParty has the responsability to pay the W/T to the tax authority on behalf of the AccountingSupplierParty.
This means that under the LegalMonetaryTotal the PayableAmount (and PayableAlternativeAmount) needs to be subtracted by the W/T total amount (this is a calculation aspect).

At this point I would see a new BIE named "PayableWithholdingTaxAmount" (0..1) under the LegalMonetaryTotal to evidence the W/T amount to be paid separately from the PayableAmount.