Document contains same order item more than once

What causes this issue?

If the following conditions are fulfilled, you can settle an order item
in an invoice received via EDI/SOA more than once:
Goods-receipt-based invoice verification has been defined for the order
item.
The delivery note numbers of the goods receipts are contained in the
IDoc or in the SOA message.
IF &[SWITCH]MM_SFWS_DINV_02&='X'.
You are using differential invoicing and one previous invoice already
exists (as of second invoice). In other words, for each goods receipt
item or purchase order item, the system displays both the current item
(invoice item) and the item from the previous invoice document (credit
memo item) in accordance with the
<DS:GLOS.4F64D5AEFB615077E10000000A421945>two-line concept</>.
ENDIF.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

System Response

If these conditions are not fulfilled, the system cancels posting of the
IDoc or the SOA message.

How to fix this error?

Check the IDoc or SOA message. You may be able to edit the IDoc or SOA
message (for example, if the supplier transmitted the wrong order item
by mistake). Otherwise, you must inform the supplier and ask for the
invoice with the corrected data to be transmitted once again.

Error message extract from SAP system. Copyright SAP SE.