Contracting Authorities : how to integrate your accounting software with the Mercurius platform?



simple eprior

In this article, you will find all the practical information you need to use your accounting (or incoming invoice) software in combination with the Mercurius platform.

The Mercurius platform makes electronic invoicing accessible to any economic operator subscribing to the rules of the Peppol interoperability framework. 

The simpl.ePRIOR web service, set up by the public authorities, allows you to send and receive messages between your accounting software and Mercurius. Its access is provided by various service integrators. 

A. The simpl.ePRIOR web service
B. Which service integrators provide access to simpl.ePRIOR?
C. How does it work?
D. Who can I contact for more information?

A. The simpl.ePRIOR web service

The Mercurius platform allows the end-to-end integration of your economic operators' invoicing tools with your accounting system.

To achieve this, the public authorities have implemented simpl.ePRIOR, a robust, standard and well-documented web service. It provides several operations for receiving and sending messages (business responses). Within the framework of the "inbound invoicing" flow, the message received contains an invoice.   

Here you will find a description of how this web service works and an explanation of the most common usage models with technical examples: Simpl.ePRIOR Technical Documentation

B. Which service integrators provide access to simpl.ePRIOR?

In application of the framework regulating public authorities' access to IT flows, your access to this web service is provided by your service integrator. 

The following integrators already provide access to simpl.ePRIOR : 

Integrator Target Audience Documentation
FSB Federal administration

Je veux me connecter | DG VD (

Webservice : ‘S331-MercuriusService (Simpl.ePRIOR)’

FIDUS Brussels Capital Region
MAGDA Flanders

Walloon Region
German-speaking Community
Federation Wallonia-Brussels

Facturation électronique - Banque Carrefour d'Échange de Données (

Contact :


Direct integration, i.e. without using a service integrator, is also possible. It is generally applicable for private law contracting authorities, i.e. Not for Profit Organisations and other organisations subject to the Public Procurement Act because of the subsidies they receive. This option can also be considered for other contracting authorities, as long as this does not contravene the agreements concluded in this area within their level of authority. For more information, please consult: Simpl.ePRIOR Technical Documentation.

C. How does it work?

The diagram below shows how end-to-end flows flow between the vendor billing system and the Contracting Authorities' accounting system when an invoice is received ("inbound invoicing" flows). 

How does Mercurius work

  1. The vendor sends the invoice, previously created in his own accounting system, via Peppol.

  2. Mercurius receives the invoice and places it in the "inbox" of the relevant contracting authority.

  3. The authority collects his incoming mail via the Mercurius service offered by his integrator. 

  4. The integrator accesses Mercurius, picks up the e-invoice on behalf of the contracting authority and sends it to the contracting authority.

Result: the e-invoice is transmitted to the contracting authority. It is removed from the contracting authority's incoming mail on Mercurius but remains visible on the Mercurius portal.

Some remarks

  • At any time, the supplier, the awarder and all intermediaries involved can monitor the progress of the transmission via the portal (reference 5 in the diagram).

  • Your supplier is not able to transmit his electronic invoice on Peppol? If it is a simple invoice, he can enter it in the portal (see 1a).

  • If your supplier has participated in the pilot phase and is not yet able to transmit his electronic invoice via Peppol, he can temporarily transmit it via the pilot interface (see 1b).

  • You are not yet able to receive e-invoices? Mercurius converts the e-invoice into a PDF document and sends it to an e-mail address that has been saved in its configuration (see 3c).

D. Who can I contact for more information?

All your questions and requests can be sent via the following channels:  

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