No backorder processing for item &1/&2

What causes this issue?

The document was not completely transferred to SAP APO.

System Response

The item &V1&/&V2& was not taken into account by backorder processing.

How to fix this error?

Enter sales order processing and change the document. The sales order
is then transferred again.

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.