Exchange assignment is not possible.

What causes this issue?

Using the exchange assignment, you assign a delivery item to a purchase
order item. The delivery item has to belong to a goods issue movement
type. You can't carry out the exchange assignment for this item,
because there is no movement on this item (for example a bill of
material header can be an item without movement in case the goods issue
is on the components).

System Response

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

How to fix this error?

Error message extract from SAP system. Copyright SAP SE.