how to default payment_method_lookup_code value in the AP_SUPPLIER_SITES_ALL table in R12.2.3

Hello,

How to default the payment_method_lookup_code value in the AP_SUPPLIER_SITES_ALL in R12.2.3; We have a custom program which creates Vendors/Vendor Sites which uses an Oracle API - pos_vendor_pub_pkg.create_vendor_site. This API does not provision us to populate the payment_method_lookup_code values for the newly created supplier sites in R12, there by populating this field as null.

These vendors/vendor sites are later being used in another custom program that imports and approves invoices from a third party source.  This program uses payment_method_lookup_code values from AP_SUPPLIER_SITES_ALL table. Since this value is null in the sites, the invoice program is not resulting in expected results. Please advise