You have won the contract, delivered the services and prepared your invoice — but the authority refuses your PDF. Reason: your invoice is not a structured electronic invoice. For many SMEs, this is the moment when e-invoicing goes from an abstract concept to an urgent problem.
Since November 2023, e-invoicing is mandatory for virtually all public contracts in Belgium above €3,000. In this article we explain what a structured e-invoice actually is, when the obligation applies, and how to adapt your invoicing process as a government supplier.
What is a structured e-invoice?
A structured electronic invoice is not a PDF and not a scan of a paper invoice. It is an invoice in a machine-readable XML format that can be automatically imported by the recipient’s accounting and payment systems.
The mandatory format in Belgium is Peppol BIS Billing 3.0, based on the European standard EN 16931. This format follows the UBL protocol (Universal Business Language) and contains all legally required data in standardised fields: VAT number, amounts, VAT rates, payment references.
The difference with a PDF: a PDF is an image of an invoice that humans can read but software cannot automatically process. A UBL invoice is the reverse — machines read them flawlessly, but you need software to view them.
When is e-invoicing mandatory?
The obligation was phased in via the Royal Decree of 9 March 2022:
- From 1 November 2022: contracts with a value from €215,000.
- From 1 May 2023: contracts with a value from €30,000.
- From 1 November 2023: contracts with a value from €3,000.
Contracts below €3,000 are exempt. The thresholds are exclusive of VAT and refer to the value of the contract, not the individual invoice.
B2B e-invoicing from 2026
From 1 January 2026, structured e-invoicing also becomes mandatory for all domestic B2B transactions between Belgian VAT-registered entities, regardless of the amount. A transition period of three months (January to March 2026) applies without sanctions. This falls outside the strict framework of public procurement, but affects the same businesses and the same systems.
The Peppol network
Peppol is the network through which structured documents (invoices, credit notes) are exchanged. It works similarly to the email system: you do not send directly to the recipient, but via an Access Point that secures, validates and forwards your invoice to the recipient’s Access Point.
To invoice via Peppol you need two things:
- A Peppol Access Point. This can be your accounting software (if it supports Peppol), a specialised service provider, or the free platform Let’s Peppol (for SMEs and freelancers).
- Your Peppol ID. This is typically your enterprise number (KBO number) through which you are findable on the network.
BOSA acts as the Peppol Authority for Belgium and oversees the certified Access Points.
Mercurius: the government’s receiving platform
Mercurius is the central platform through which Belgian government services receive and process e-invoices. It functions as the electronic mailbox for all federal, regional and local authorities.
As a supplier, you send your invoices not directly to the authority’s email address, but via Peppol to Mercurius. The platform routes the invoice to the correct department and gives you the ability to track the status of your invoice.
The Mercurius portal also offers a manual option: if your invoicing software does not support Peppol, you can create invoices and credit notes manually via the Mercurius web interface. This is an emergency solution for small suppliers, but not suitable for structural use.
Onboarding for SMEs
Step 1: Check your software
Most modern accounting software packages now support Peppol. Check with your software vendor whether your package can generate UBL invoices and send them via Peppol. Major providers like Exact, Billit, Yuki and Octopus offer this functionality as standard.
Step 2: Choose an Access Point
If your software does not support Peppol directly, choose an external Access Point. Let’s Peppol is a free, open-source solution supported by the non-profit BARGE, specifically aimed at SMEs and freelancers. Commercial alternatives offer more features (automatic matching, ERP integration).
Step 3: Register your Peppol ID
You are registered on the Peppol network once you have an Access Point. Check on the Mercurius portal whether your organisation is correctly registered as both receiver and sender.
Step 4: Test with a government service
Send a test invoice to a government service you already have a contract with. Check via Mercurius whether the invoice was correctly received and processed.
Common mistakes
Treating PDFs as e-invoices. A PDF is not a structured e-invoice, even if you send it by email. The authority may refuse a PDF if the specifications require a structured e-invoice.
Wrong reference on the invoice. The specifications typically prescribe which reference must appear on the invoice (purchase order number, contract number). An invoice without the correct reference is not automatically matched and delays payment.
Starting too late. Peppol onboarding takes time: software check, choosing an Access Point, registration, tests. Do not start this at the moment you need to send your first invoice.
Forgetting credit notes. Credit notes must also be sent as structured e-invoices via Peppol. A credit note by PDF while the invoice went via Peppol causes processing problems for the recipient.