Attachment field not visible on ESC portal form

We are working on an Expense Management project using the Employee Center (ESC) portal in ServiceNow. Employees submit expense line items using a form based on the custom table x_merl4_expense_ma_line_of_items.

When the request is returned by the approver (state: Returned for Review), the user should be able to edit certain fields and also upload attachments. The attachment field has been added to the backend form layout. There are no UI policies or client scripts hiding it. However, on the ESC portal, the attachment section is not visible even though the form is editable. We are not using the classic service portal. Has anyone faced this issue or knows how to make the attachment section appear in this scenario?