R121.3: AP: SLA Setup - How Can I Assign a Custom Source to the GL Date Accounting Attribute

How can be assigned a custom source to 'GL Date' accounting attribute?

We would like to add that for AP invoices event class.

We are going to implement a secondary ledger and close it earlier than the primary ledger.

So, we will need to create accounting entries in the Secondary Ledger on the Secondary Ledger Date from the Invoice Distribution DFF.

I reviewed the Note Doc ID 2137886.1 and created a PL/SQL function accordingly.

However, my custom source does not appear in the list of values in the Accounting Attributes Assignments in the Source filed.

Thank you in advance for any ideas.