Purchasing document item &1 &2 is returns item

What causes this issue?

You have entered a purchasing item as predecessor for an inbound
delivery item. This purchasing item is a returns item.
Returns items are not allowed as predecessors for inbound delivery
items.

System Response

The inbound delivery cannot be posted.

How to fix this error?

Enter a valid purchasing document.

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.