No valid item relevant for differential invoicing is selected

What causes this issue?

IF &[SWITCH]MM_SFWS_DINV_02& = 'X'.
You are trying to post a provisional invoice, differential invoice, or
final invoice, but no item relevant for differential invoicing has been
selected in the invoice.
ELSE.
You are trying to post a provisional invoice, differential invoice, or
final invoice, but no item relevant for differential invoicing has been
selected in the invoice.
ENDIF.

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?

Select at least one item that is relevant for differential invoicing in
the invoice.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.