How to use a Sandbox to prevent duplicate invoice creation using the same charge reference in LCM

Summary:

When following the Landed Cost Management (LCM) process in Oracle Fusion, the same charge reference value from trade operation lines can currently be used in multiple invoices.

However, the requirement is to prevent the creation of multiple invoices using the same charge reference value.

To address this, we are planning to use a Sandbox and develop an EL Expression on the Invoice Creation page to restrict duplicate usage of a charge reference. Specifically, if a charge reference value has already been used in an invoice, the system should not allow it to be selected or entered again.

Could you please advise how we can develop and apply the required EL Expression using the Sandbox to achieve this functionality?