To Enable DFF on payment process Request in OAF page

The right DFF is "Invoice Selection" under application "Payables"

You can check the DFF in OA page in the following way:
Go to the target page.
Eg: Payments > Entry > Payment Manager
Payment Process Requests.
About this Page
Flexfield References
Flexfield Name = "AP_INVOICE_SELECTION_CRITERIA"
Go to Setup > Flexfields > Descriptive > Register
Query with the Name "AP_INVOICE_SELECTION_CRITERIA"
Note down the Application and Title

-- To implement the solution, please execute the following steps
1. Go into the responsibility: Payables Responsibility

2. Navigate to Setup > Flexfields > Descriptive > Segments

3. Query for Application Payables and Title Invoice Selection

4. Unfreeze the structure and Define a Context sensitive DFF code and segments required.

5. Freeze the Flexfiels Definition and Compile it

6. Retest the issue

7. Migrate the solution as appropriate to other environments