Item to be picked by WM (picking quantity cannot be entered)

What causes this issue?

For this item, <GL:picking>picking</> is carried out using
<GL:warehouse_management_system>warehouse management</> transfer orders
since the material is stored in a warehouse with random storage.

System Response

The system does not allow you to enter a picking quantity manually. The
picking quantity is copied automatically into the delivery during the
creation of the corresponding transfer order.

Error message extract from SAP system. Copyright SAP SE.