> ## Knowledge Base Index
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> Use this file to discover available pages before exploring further.
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# How does the duplicate detection work?

To prevent fraud, Klippa uses automatic detection of duplicate invoices. We use a few techniques to mark a transaction as a possible duplicate:
1. We look at the document, whether we have seen the exact same document results before in our system
2. We look at the combination of certain fields

###### Invoices
We mark as duplicate if 2 out of 2 fields are the same:
* Invoice number + merchant
* Invoice number + amount

###### Expenses
We mark as duplicate if 3 out of 4 fields are the same:
* Merchant
* Invoice number
* Amount
* Date

|| Info: We also check the OCR results (so if someone edits the fields it’s still flagged)

| Tip: When a transaction is flagged as possible duplicate, you can click on the description given in bold letters within the notification to open the possible duplicate transaction

###### Example of possible duplicate transactions

1. Notification 'possible duplicate of X on date Y' when opening the invoice.

![](https://storage.crisp.chat/users/helpdesk/website/4cae8d8acec84400/screenshot-2024-04-03-at-11302_2v5kln.png)

2. Notification 'possible duplicate of X on date Y' in the overview of all invoices.

![](https://storage.crisp.chat/users/helpdesk/website/4cae8d8acec84400/screenshot-2024-04-03-at-11310_9pqni2.png)
||| Note: Despite the notification of a possible duplicate, an invoice can still be exported or booked.