Item &1: The original order item has already been invoiced

What causes this issue?

The order item that is the basis for the current item &V1& has already
been billed. The <DS:GLOS.3526C71FAFAB52B9E10000009B38F974>billing
document</> was created, taking into account the delivery quantities (
<DS:DE.FKREL>billing-relevance</>).
IF &[SWITCH]S4H_DOCU_ON_PREMISE& = 'X'.

System Response

Changing the delivery quantity or deleting the item causes an
inconsistency between the billing documemt and the delivery. Depending
on your Customizing settings, the system rejects the requested change or
issues a message telling you when this situation can be tolerated in
your system.
ENDIF.

How to fix this error?

Where necessary, cancel the billing document before you make the
required changes to the delivery.
IF &[SWITCH]S4H_DOCU_ON_PREMISE& = 'X'.

Procedure for System Administrators

You can control billing-relevance of the delivery item in Customizing
for the <DS:GLOS.3526C751AFAB52B9E10000009B38F974>order item category
</> of the same name.
To do this, choose Customizing for Sales and Distribution: <ZK>Sales</>
--> <ZK>Sales Documents</> --> <ZK>Sales Document Item</> -->
<DS:SIMG.SIMG_CFMENUOLSDVOV7>Define Item Categories</>.
You can also specify the characteristics of this message in Customizing.
To do this, choose Customizing for Logistics Execution: <ZK>Shipping
</> --> <ZK>System Modifications</> -->
<DS:SIMG.SIMG_CFMENUOLSDOVM1>Specify Characteristics for System Messages
</>.
ENDIF.

Error message extract from SAP system. Copyright SAP SE.