Need Guidance on Mapping Employee Numbers in OTBI Expense-to-Payables Reporting

Summary:

We have developed an OTBI report using the Payables subject area to retrieve invoices imported from Expenses and to track the payment status of those expense-related invoices. However, we are unable to include the employee number in the report because this attribute is not available within the Payables subject area.

We attempted to supplement the report by using the HCM (Workforce Management) subject area to fetch the employee number, but we were unable to successfully combine the data from both subject areas.

Could anyone advise on the recommended approach for retrieving the employee number for expense invoices within OTBI, or suggest an alternative method for achieving this requirement?