# Duplicate Invoice Detection Before Payment | InvoiceIQ AP by Analytos

> InvoiceIQ AP by Analytos checks for duplicates twice: once when the match report is built, and again at the moment of posting. Invoice numbers are…

Canonical URL: https://invoiceiq.analytos.ai/ap/duplicate-detection

Duplicate detection

# Duplicate detection  
before the bill posts

Duplicate invoices are caught twice, once when the invoice is checked and again at the moment of posting.

[Book a walkthrough](https://invoiceiq.analytos.ai/contact)[InvoiceIQ AP by Analytos](https://invoiceiq.analytos.ai/ap)

The question: How can AP detect duplicate invoices before payment?

## The short answer

InvoiceIQ AP by Analytos checks for duplicates twice: once when the match report is built, and again at the moment of posting. Invoice numbers are normalised first, so “VS-4410”, “vs 4410” and “VS4410” are the same invoice. A purchase order that is already fully billed is also raised as a possible duplicate. Duplicates are blocked, never quietly paid.

## How it works

1.  Step 1
    
    Normalise
    
    Strip case, spaces and punctuation from the invoice number.
    
2.  Step 2
    
    Compare
    
    Check the vendor and normalised number against invoices already processed.
    
3.  Step 3
    
    Check the order
    
    Flag a PO that has already been billed in full.
    
4.  Step 4
    
    Re-check at posting
    
    Run the guard again at the moment of posting, in case a copy arrived meanwhile.
    
5.  Step 5
    
    Block and explain
    
    Hold the invoice with the earlier match named.
    

## Why duplicates slip through

-   The same invoice is emailed twice, or emailed and uploaded.
-   A reminder copy is sent with a slightly different number format.
-   A second person keys an invoice already in someone else’s queue.

## Controls

-   Exactly-once email intake: a message-id ledger means the same email is never ingested twice
-   The duplicate guard cannot be bypassed by switching policy
-   Every refusal is on the Posting Log

## Is this a fit?

### A good fit when

-   Invoices arrive by several channels
-   Several people process the same vendors

### Not the right tool when

-   You need cross-entity duplicate detection across separate ERPs (scope it with us)

## Evidence

-   CapabilityNormalised duplicate guard on the report and again at posting.

How we label claims: [evidence and claims policy](https://invoiceiq.analytos.ai/resources/evidence).

## Frequently asked  
questions

-   ### 
    
    Yes. Numbers are normalised before comparison.
    
-   ### 
    
    It is held for review with the earlier invoice shown, so a person decides.
    
-   ### 
    
    The duplicate guard runs under every policy, including the non-PO tier.
    

## Related questions

[InvoiceIQ AP by AnalytosAI Accounts Payable Automation](https://invoiceiq.analytos.ai/ap)[Invoice exception managementHow do I reduce invoice exceptions and clear the AP exception queue faster?](https://invoiceiq.analytos.ai/ap/exception-management)[AP controls and audit trailWhat controls should AP automation have?](https://invoiceiq.analytos.ai/ap/controls-governance)[3-way invoice matchingHow do I automate invoice matching against the PO and the goods receipt?](https://invoiceiq.analytos.ai/ap/3-way-matching)

## See InvoiceIQ AP on your own documents

InvoiceIQ AP by Analytos: ai accounts payable automation. A walkthrough starts with your real supplier invoices, purchase orders and receipts.

[Book a walkthrough](https://invoiceiq.analytos.ai/contact)