If workflow is defined for Bill payments, the file will go for approval to the approver. The approver can go to the below path and click on the file name to download the file. The downloaded file will have the outstanding against each consumer number.
Dashboard > Pending on Me > Bulk Payments or Transfers and Bill Pay > Transaction Approvals > Pending on Me > Bulk Payments.
If the workflow is not enabled for Bill payments, then once the outstanding gets fetched from the Biller, the file will go directly for payments and the outstanding amount will be available under the reverse MIS.