Electronic Invoicing: Complete Definition and Guide

What is Electronic Invoicing?

Electronic invoicing, or e-invoicing, refers to the complete process of issuing, transmitting and receiving invoices in a structured digital format directly processable by both the sender's and recipient's IT systems. This is not simply sending a PDF by email: an electronic invoice in the legal sense is a structured document (typically in UBL or Peppol BIS format) that travels through a secure exchange network and whose data can be automatically integrated into accounting software without manual re-entry.

In Belgium and the European Union, electronic invoicing is experiencing unprecedented regulatory acceleration. The mandatory B2B electronic invoicing obligation takes effect in Belgium from January 1, 2026. This requirement, in addition to the already existing B2G (Business to Government) obligation, will radically transform invoicing practices across the entire Belgian economic fabric.

KERN-IT anticipated this transformation by developing PeppolOutbox, a SaaS electronic invoicing solution that enables Belgian companies to issue and receive compliant invoices on the PEPPOL network. This hands-on expertise gives us a concrete vision of the challenges and issues involved in the transition to electronic invoicing.

Why Electronic Invoicing Matters

Adopting electronic invoicing goes far beyond simply meeting a legal obligation. It represents an opportunity for profound transformation of the invoicing cycle with measurable benefits:

• Regulatory compliance: from 2026, all VAT-registered businesses in Belgium must be able to issue and receive structured electronic invoices. Failing to prepare exposes companies to penalties and an inability to invoice clients.
• Cost reduction: manually processing a paper invoice costs an average of 10 to 30 euros (printing, mailing, receiving, data entry, archiving). An electronic invoice reduces this cost to less than 1 euro through complete cycle automation.
• Payment acceleration: electronic invoices are received instantly and automatically integrated into the recipient's accounting system. Processing times drop from several days to minutes, accelerating the payment cycle.
• Error reduction: eliminating manual data entry removes transcription errors that cause disputes, payment delays and correction costs.
• Complete traceability: every invoice is tracked end to end: issuance, transmission, reception and acknowledgment. In case of disputes, the history is complete and indisputable.
• Environmental impact: eliminating paper, ink and postal transport significantly reduces the carbon footprint of the invoicing process.

How It Works

Electronic invoicing relies on a technological ecosystem composed of three key elements: the structured format, the transmission network and the access points.

The structured format is the foundation. In Europe, the reference format is UBL (Universal Business Language) 2.1, implemented in the Peppol BIS Billing 3.0 specification. Unlike a PDF, which is a human-readable image, a UBL file is an XML document where every data element (invoice number, net amount, VAT rate, customer references) is tagged and structured in a standardized way. This allows IT systems to automatically read, validate and integrate information without human intervention.

The transmission network in Belgium is the PEPPOL network (Pan-European Public Procurement OnLine). This network operates on a four-corner model: the sender transmits the invoice to their PEPPOL access point, which forwards it to the recipient's access point, which delivers it to the recipient. This model ensures each participant only needs a single connection to an access point to exchange with all other network participants.

Access points are certified providers authorized by the PEPPOL authority that handle secure document transmission. PeppolOutbox, developed by KERN-IT, is a certified PEPPOL access point that offers a simplified interface for businesses: invoice creation via web form or import from accounting software, automatic network submission, and incoming invoice reception and archiving.

Concrete Example

Consider a 25-person Brussels SME specializing in industrial maintenance services. This company issues approximately 200 invoices per month and receives about 100. Before its transition to electronic invoicing, the process looked like this: the accountant generated invoices in accounting software, exported them as PDFs, sent them by email with a personalized message, then printed and filed a paper copy. On the receiving side, supplier invoices arrived by email or mail, were printed, manually verified and entered into the accounting software.

By adopting PeppolOutbox and connecting the accounting software via API, this SME radically transformed its process. Invoices are now generated in UBL format directly from the accounting software and sent automatically on the PEPPOL network. Recipients receive them within seconds, and an acknowledgment confirms successful delivery. Incoming invoices are automatically retrieved and integrated into accounting with automatic data recognition.

Results after six months: time spent on invoicing was reduced by 75%, data entry errors virtually disappeared, average client payment time decreased by 12 days, and the company is already compliant with the 2026 legal obligation, two years ahead of schedule.

Implementation

1. Current invoicing process audit: map the complete invoicing flow (issuance and reception), identify volumes, formats used, tools involved and friction points.
2. Accounting software compatibility check: verify whether the existing accounting software supports UBL export and API integration. If not, evaluate update or replacement options.
3. PEPPOL access point selection: choose a certified access point that matches the company's size and needs. KERN-IT's PeppolOutbox offers a solution tailored to Belgian SMEs with an intuitive interface and French-language support.
4. PEPPOL network registration: register the company in the PEPPOL directory with its BCE enterprise number, enabling other participants to send electronic invoices.
5. Configuration and testing: set up the integration between accounting software and the access point, then conduct send and receive tests with pilot partners.
6. Progressive deployment: start with clients and suppliers already on the PEPPOL network, then gradually expand to all business partners.

Associated Technologies and Tools

• UBL 2.1 (Universal Business Language): the European standard XML format for structured commercial documents, including invoices, credit notes and purchase orders.
• PEPPOL network: a secure communication infrastructure for exchanging electronic commercial documents between businesses and public administrations across Europe.
• REST APIs: programming interfaces that connect existing accounting software to PEPPOL access points for automated invoice sending and receiving.
• Python and Django: technologies used by KERN-IT to develop PeppolOutbox, offering robustness, security and flexibility for commercial document processing.
• PostgreSQL: a relational database for secure and compliant electronic invoice archiving with the legally required 7-year retention period in Belgium.

Conclusion

Electronic invoicing is no longer optional in Belgium: it is an obligation taking effect in 2026 for all B2B transactions. But beyond the regulatory constraint, it is a major optimization opportunity for any business processing a significant volume of invoices. KERN-IT, through PeppolOutbox, supports Belgian companies in this transition with a solution that combines ease of use, full compliance and integration with existing tools. Not waiting until 2026 is the best advice we can give: companies preparing today are already reaping the benefits.