Belgian B2G and Mercurius: how it differs from B2B Peppol
Orientation playbook for Belgian public-sector e-invoicing via Mercurius versus the private B2B Peppol mandate, with a practical SME checklist.
Updated
- Belgium
What this playbook covers
Belgium runs two Peppol-related worlds that SMEs often mix up:
- B2G (business to government): structured invoices to public entities, typically via the federal Mercurius platform on Peppol
- B2B (business to business): structured invoices between private VAT-liable parties under the domestic mandate from 2026
Same network family, different buyers, routing, and compliance drivers. For private-mandate scope, start with the Belgian B2B e-invoicing obligation.
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 any buyer-specific fields before go-live |
| You only sell to private companies | Mercurius is usually not your daily path; focus on B2B Peppol |
Mercurius is the Belgian federal hub that helps public administrations receive Peppol invoices. Your software still talks Peppol through an Access Point; Mercurius is the public-side reception layer, not a replacement for your own Peppol setup.
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 idea | Structured send toward the public Peppol identity (Mercurius-backed) | Peer-to-peer Peppol between businesses |
| Format baseline | Structured EN 16931-style invoice (see EN 16931 and UBL) | Same structured family for in-scope B2B |
| 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. B2G readiness and B2B readiness overlap technically, but the obligation scopes differ.
Practical SME posture
Most Belgian SMEs fall into one of three postures:
| 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 |
Operational checklist:
- Tag each customer: public entity, Belgian VAT-liable B2B, or other
- Store the correct Peppol participant ID per public buyer
- Validate structured invoices before send (same discipline as private Peppol)
- Keep delivery evidence and the structured original (invoice archiving)
- Train sales/finance: public PO references and private B2B rules are different intake forms, not the same ticket
Related reading
- Network basics: What is Peppol?
- Channel choice: PDF vs structured invoice
- Private mandate: Belgian B2B e-invoicing obligation