How to update "Discountable Amount" in Invoice Installments via REST API?

Hi Experts,

I am working with Oracle Fusion ERP Cloud – Payables Invoice REST APIs.

I need to update the Discountable Amount field under Manage Installments for an invoice. I searched the Invoice Installments REST API, but I could not find this field exposed in the payload.

Requirement:

• Update the Discountable Amount for an existing invoice installment.
• Perform the update through REST API (not manually in the UI).
• See image below For that field