Fixed Item Quantity not possible together with "Accept Remaining Qty"

What causes this issue?

The flag for distribution of remaining stock for the current item is
<LS>Accept Remaining Stock</>, and <LS>Fixed Item Quantity</> was
selected as a parameter.
The system cannot distribute remaining stocks with this combination.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Either remove the <LS>Fixed Item Quantity</> flag to execute the
allocation strategy or cancel the allocation strategy, change the flag
for distribution of remaining stock in the item details, and execute the
allocation strategy again.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.