Item &: planned qty is & than allocated quantity - automatic adjustment

What causes this issue?

The system has automatically allocated the planned quantity for an item
entered by the user among the plants. The quantity allocated now
differs from the quantity entered by the user.
This occurs in the following cases:

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

The "reminaing quantity" parameter is set to "Accept remainder".
Here the system accepts the remainders and adjusts the total quantity.
The "Round off" parameter is set to "Order optimizing".
Here the system rounded off the order quantities, resulting in the
total quantity entered differing from the optimized quantity. The
system cannot allocate the differences automatically.

System Response

The system uses the allocated quantity as the new planned quantity.

How to fix this error?

Edit the quantities allocated by the system.

Error message extract from SAP system. Copyright SAP SE.