Belgian B2G and Mercurius: how it differs from B2B Peppol
Mercurius is the federal platform that receives structured invoices for Belgian public entities. Portal for occasional send, Peppol for the SME, API for the contracting authority. It is not your Access Point.
Updated
- Belgium
Belgium runs two Peppol-related worlds that SMEs often mix up: B2G (structured invoices to public entities, typically via the federal Mercurius platform) and B2B (structured invoices between private VAT-liable parties under the domestic mandate from 2026). Same network family, different buyers and compliance drivers. For private-mandate scope, start with the Belgian B2B e-invoicing obligation.
Official overview: e-invoice Belgium.
When the public-sector path applies
| Signal | Practical meaning |
|---|---|
| Buyer is a Belgian public entity | Expect a B2G channel, not a private AP email inbox |
| Buyer publishes a Peppol / Mercurius identity | You send a structured invoice via an Access Point |
| Contract or PO references a public buyer | Confirm their Peppol ID and buyer-specific fields before go-live |
| You only sell to private companies | Mercurius is usually not your daily path; focus on B2B Peppol |
- Mercurius platform
Federal reception hub for structured invoices destined to participating Belgian public entities. Your software still talks Peppol through a certified Access Point. Mercurius is not that Access Point.
Portal versus API
Mercurius is a platform. SMEs meet it in three different ways. Do not treat them as one login.
| Channel | Who uses it | What it does |
|---|---|---|
| Mercurius portal | Occasional supplier without Peppol; also track-and-trace | Encode or upload a simple invoice; follow status |
| Peppol via Access Point | SME with invoicing software (normal path) | Send BIS Billing to the public Peppol ID; Mercurius receives on the public side |
| API (simpl.ePRIOR) | Contracting authorities, via a service integrator (FSB / MAGDA / FIDUS or equivalent) | Connect the administration’s accounting software to Mercurius |
The Mercurius API is not an SME project. You do not call simpl.ePRIOR to invoice a commune. You send through Peppol. If you have no Access Point yet, the portal can carry a simple invoice. That is not a 2026 B2B channel.
How an SME sends in practice:
- Tag the buyer as a public entity.
- Store the Peppol ID they publish (often Mercurius-backed).
- Issue a structured invoice (see EN 16931 and UBL).
- Send via your Access Point, not PDF-only email.
- Keep delivery evidence and the structured original (invoice archiving).
- Open the portal only if you lack Peppol, or for status tracking.
B2G / Mercurius versus private B2B Peppol
| Topic | B2G (Mercurius path) | Private B2B Peppol |
|---|---|---|
| Counterparty | Public administrations and related bodies | Private VAT-liable businesses |
| Driver | Public procurement / B2G e-invoicing rules | Domestic B2B structured mandate from 2026 |
| Routing | Structured send toward the public Peppol identity (Mercurius-backed) | Peer-to-peer Peppol between businesses |
| Your Access Point | Still yours, for send | Yours, for send and receive |
| PDF-only email | Wrong channel for covered public buyers | Wrong channel for in-scope B2B from 2026 |
Do not treat “we already invoice one commune on Peppol” as proof that your entire private customer base is covered for 2026. The obligation scopes differ.
Mercurius is not your Access Point
| Mistake | Reality |
|---|---|
| “I signed up on Mercurius, so I am on Peppol” | The portal serves B2G. Peppol registration for private B2B is a separate publication |
| “Mercurius is my Access Point” | The Access Point connects your company. Mercurius is the public-side reception layer |
| “The Mercurius API replaces my invoicing tool” | The API ties the administration to Mercurius, not your daily billing |
Practical SME posture
| Your mix | Priority |
|---|---|
| Public buyers only or mainly | Get Peppol send working for Mercurius / public IDs first; keep registration clean |
| Private B2B only | Prioritise Peppol registration, send and receive for 2026 |
| Mixed public + private | One Peppol identity, two process tracks: public buyer rules vs private mandate counterparties |
Worked example
Atelier Nord SRL invoices the commune of Xelnes, PO COM-2026-441. The software sends a structured invoice to the commune’s Peppol ID. Mercurius receives on the public side. Atelier Nord does not live in the portal and does not integrate simpl.ePRIOR. Private customers stay on the 2026 B2B Peppol path.
Related reading
- Network basics: What is Peppol?
- Channel choice: PDF vs structured invoice
- Private mandate: Belgian B2B e-invoicing obligation
FAQ
What is the Mercurius platform?
The federal hub that receives structured invoices for participating Belgian public entities, connected to Peppol.
What is the difference between the Mercurius portal and the API?
The portal is occasional encoding and track-and-trace. The API (simpl.ePRIOR) connects the contracting authority’s software to Mercurius via a service integrator.
How does an SME send a B2G invoice?
Through its Peppol Access Point to the public ID. The portal is only a fallback if the SME has no Peppol yet.
Is Mercurius a Peppol Access Point?
No. Your Access Point connects you to the network. Mercurius is reception on the administration side.
Do I need a Mercurius account for B2B 2026?
No. The private mandate runs through Peppol registration and an Access Point, not a Mercurius portal login.
Should an SME use the Mercurius Peppol API?
No. That API is the administrations’ web service. The SME sends Peppol from its invoicing software.
Is PDF by email enough for a public buyer?
No when the buyer requires a structured e-invoice. See PDF versus structured invoice.
Does invoicing one commune cover my private customers?
No. B2G and B2B obligation scopes differ, even though the network family is the same.