Order quantity is smaller than delivered quantity

What causes this issue?

The order quantity which you have entered is smaller than the quantity
already delivered to stock for this order.

System Response

There are two possibilities:
If the difference between the two quantities is within the overdelivery
tolerance, the system issues a warning message.
If the difference betweeen the two quantities is larger than the over-
delivery tolerance, the system issues an error message.

How to fix this error?

If you received a warning, you can decide whether to ignore the message
or to change the order quantity.
If you received an error message, you have to change the order
quantity.

Error message extract from SAP system. Copyright SAP SE.