No negative quantity specification allowed for non-stock materials

What causes this issue?

You have entered a negative quantity entry for a non-stock material.
This is not allowed.

System Response

INCLUDE KEINE-VERARBEITUNG OBJECT DOKU ID TX LANGUAGE EN

How to fix this error?

If you want to return the ordered non-stock material to the
<DS:GLOS.vendor>vendors</>, you must enter a return delivery to the
vendors for the <DS:GLOS.purchase_order>purchase order</>, for the
<DS:GLOS.goods_receipt>goods receipt</>.

Error message extract from SAP system. Copyright SAP SE.