How to calculate withholding tax in FB60 uploading using bapi?

Hi Experts,

Im very new to the world of SAP and ABAP Programming. Just joined a job and have a very tough task given on the very first day.

There is a Uploading done for transaction FB60 using BAPI .

Bapi used is BAPI_ACC_DOCUMENT_POST and BAPI_TRANSACTION_COMMIT .

Its working perfectly fine but now they have asked me to make changes in it so that the withholding tax is also calculated and deducted.

Im providing the current program please guide me how and what changes i hv to make?

Sinse im very new to ABAP itself and the task given to me is very tough so please i would would warm welcome all support and help i get.

Regards,

Harish Khandelwal