&1 is already packed: Quantity reduction under &2 is not possible

What causes this issue?

You want to reduce the quantity in the inbound delivery item. However,
&v1& are already packed and you cannot reduce the packed quantity.

System Response

The system does not allow you to reduce the quantity.

How to fix this error?

Unpack the packed quantity when you want to reduce the quantity.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.