In the "mat.to be prov." items, the quantity is set to zero

What causes this issue?

You have set the goods receipt quantity to zero.

System Response

The system automatically adjusts the quantity in the "material to be
provided" items of this purchase order item. This means that no goods
issue is posted from the stock of material provided (to vendor).


Hinweis
If you change the goods receipt quantity once more, the system will not
again adjust the quantity in the "material to be provided" items. You
will then have to correct the "material to be provided" items manually.

Error message extract from SAP system. Copyright SAP SE.