Duplicate supplier invoices in construction: stop double project costs

Duplicates rarely look perfectly identical

A supplier invoice may arrive through Peppol, email and a site upload. The readable PDF can have a new filename while the structured invoice retains the same number. A corrected document may reuse a reference but change the amount. Reliable control therefore combines exact matching with explainable similarity checks.

Preserve every incoming source and assign an intake identifier. Normalize supplier enterprise or VAT number, invoice number, issue date, currency and totals without overwriting the original values. First flag exact combinations. Then look for near matches such as punctuation differences, leading zeros, same amount and date, or the same purchase-order reference.

Show why an item was flagged

The reviewer should see both documents side by side and a list of matching fields. Do not silently delete the later arrival. It may be a legitimate reminder copy, a corrected invoice, a staged billing document or an attempted duplicate. Keep statuses such as suspected duplicate, confirmed duplicate, related correction and distinct charge.

Use line items and project context to resolve uncertainty. Two invoices with the same total can cover different deliveries. One invoice split across several projects is still one payable document. A supplier credit note should link to the original charge instead of being treated as a negative duplicate.

Block downstream duplication safely

While review is open, stop the candidate from creating a second project cost, accounting export or payment proposal. Do not block the already approved document unless the reviewer finds a real issue. Record who released or rejected the candidate and why.

Run another duplicate check before payment because a record may enter through accounting after the project inbox review. Match bank and settlement data back to the approved invoice. If a duplicate was paid, preserve the incident trail and handle recovery through the company's finance process.

Use Peppol data without overclaiming

Belgium's structured B2B invoicing framework improves machine-readable identification, but it does not remove the need for business controls. The official FAQ explicitly discusses duplicate invoices as a practical Peppol question. Software should use structured fields and transmission identifiers while still accounting for corrections and multiple channels.

Finally, measure recurring causes: supplier resends, shared inbox forwarding, failed status feedback or manual re-entry. Fix the route rather than relying only on stronger blocking.

Connect the control with AI supplier-invoice cost coding, construction job costing and digital invoice archiving.

Sources: Belgian specific e-invoicing FAQ and current Enfin invoice-intake workflows, checked 1 August 2026.