Unable to delete transaction from post batch, SQL error received

The transaction detail line is posted. So you are unable to delete the transaction.The Invoice needs to be posted completely and then you will need to post a credit note to reverse it. As the Detail line is posted you cannot delete the transaction and cannot unflag it in the backend either, because the transaction is 50% completed and waiting for the other 50% to be completed.
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Once you post this invoice, then the transaction will be completed. And then you can post a credit note to adjust the balance.