You use SGL indicator &1 in document line &2

What causes this issue?

You post an invoice with a special general ledger indicator (e.g. down
payment, bill of exchange). You should only use the special G/L
indicator to use alternative reconciliation accounts in the G/L.
However, it should not be used to classify documents.
Note the following restriction when posting invoices with the special
G/L indicator. Down payments that refer to such invoices cannot be
updated with the <LS>Payment Selection</> program in Funds Management.

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?

Post the invoice without the special G/L indicator or do not post
payments for this invoice as partial payments.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.