Double invoice check in SAP

SAP provides multiple controls in the area of Accounts Payable. One of them refers to the possibility of entering an invoice twice and therefore, resulting in multiple payments for the same purchase. While, it is not possible for SAP to definitively conclude that an invoice is 'duplicate', it can assist to identify 'potential duplicate' invoice based on certain parameters set in the system.
This is controlled through the 'double invoice check' indicator in the vendor master record. If this indicator is set for a vendor, it means that incoming invoices and credit memos are checked for double entries at the time of entry. In this case, SAP checks whether the invoice documents have already been entered in the Logistics invoice verification. In checking for duplicate invoices, SAP compares the following characteristics by default:
1. Vendor
2. Currency
3. Company code
4. Gross amount of the invoice
5. Reference document number
6. Invoice document date.
If all of these characteristics are the same, the system issues a message that can be customized. SAP only checks for duplicate invoices in Materials Management if you enter the reference document number upon entering the invoice.

In Customizing for the Logistics invoice verification, the following characteristics can be disabled for duplicate invoice checks:

1. Company code

2. Reference document number
3. Invoice document date.
This means that you can increase the likelihood that SAP will find a duplicate invoice, because you can reduce the number of characteristics checked.

SAP then checks whether there are FI or Accounting documents that were created with the original invoice verification or the Logistics verification, and where the relevant criteria are the same. Depending on the entry in the field "Reference", one of the following checks is carried out:

1. If a reference number was specified in the sequential invoice/ credit memo, SAP checks whether an invoice/credit memo has been posted where all the following attributes agree:
    a. Company code
   b. Vendor
    c. Currency
   d. Document date
   e. Reference number.
2. If no reference number was specified in the sequential invoice/ credit memo, the system checks whether an invoice/credit memo has been posted where all the following attributes agree:
   a. Company code
   b. Vendor
   c. Currency
   d. Document date
   e. Amount in document currency.

As a good practice, you should ensure that 'double invoice check' indicator is set as a 'mandatory' field in the vendor master configuration. This ensures that the indicator is set for all vendors. Alternatively, perform data analytics to ensure that this field is set for all vendors.
Then, check the duplicate invoice check configuration parameters to determine whether any of the three configurable parameters (i.e., Company code, Reference document number and Invoice document date) have been disabled (the more parameters disabled, better is the control).