How the payment of withheld tax (On Supplies, Services and Salaries) is made in ERP Oracle R12 using the GL module?

Itis the amount with held while making the payment to the payee and it will be paid to the tax authorities.

We may be required to withhold taxes from your employee expense reports and supplier invoices. Once you set up Payables to automatically withhold tax, you can withhold tax either during Approval or during payment processing. You can control all withholding tax options in the Withholding Tax region of the Payables Options window.

i think you need to return to your system implementor, since income tax on payroll comes from HR submodule and withheld tax on purchased goods and services comes from AP submodule also beer in mind that under oracle all payments shall be issued from AP submodule not GL.