Assign bank to suppliers

Hello,

I am using the following API to assign bank to supplier. The API is not ending with errors and return the x_assign_id value successfully. 

But the bank is not getting associated to the supplier when verified through applications or in the database tables.

Can anyone please suggest if I am missing anything

                     l_rec.payment_function := 'PAYABLES_DISB';

                     l_rec.party_id := 123;

                     l_rec.Supplier_Site_id:= 456 ; 

                       l_rec.Org_Id:= 000;

                       l_rec.Org_Type:=  'OPERATING_UNIT';

                       l_rec.Party_Site_id:=789 ;--<party site ID>

                     v_instrument_rec.instrument_id := 123

                     v_instrument_rec.instrument_type := 'BANKACCOUNT';