Material &1 in plant &2 is APO-relevant

What causes this issue?

The material/plant combination is APO-relevant.

System Response

This kind of combination must be processed in the connected APO system.

How to fix this error?

Use the backorder processing tools for this material/plant combination
in the connected APO system.

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.