How to get a shipment line to backorder that has a fulfilment line in failed reservation

Summary:

Cancel the Backorder is the requirement.

Available to reserve 300

Ordered 1000

1 Line split into 2 fulfilment lines of 300 and 700.

300 line - awaiting shipping good

700 - scheduled in line and reservation failed.

Release the whole order by creating pick wave

300 lines is released which is fine.

Problem 1: There is no available quantity to reserve for 700 hence fulfilment line is in error for reservation. How to create a backorder for 700 case in shipment lines. We need a way to cancel the backorder line. Currently only 300 is released and no backorder lines found for 700.

Problem 2: After adding inventory 100, tried running recover error for the order but nothing happens - still failing for reservation on 700 line why is partial reservation not working to reserve 100 and split the order line to 100 and 600?