The Peppol five-corner model

The Peppol four-corner model gives a buyer and a seller a clean way to exchange a structured invoice without bilateral integration. It works because every Access Point on the network speaks the same standard format (Peppol BIS Billing 3.0 on top of UBL 2.1) and shares the same discovery layer (SML and SMP). When a tax authority is added, two things change.

A fifth corner appears in the architecture: the national tax administration. In Belgium this is FPS Finance; in France a central public portal sits behind the network of certified PDPs; in other EU member states, ViDA-aligned authorities will play a similar role.

The Access Points gain a reporting responsibility. As an invoice flows from corner 2 to corner 3, both Access Points also send a copy or a structured summary of the invoice to the tax authority. The reporting message is separate from the trading message: the buyer still receives the original invoice the way they always did, and the tax administration receives its own near real-time view in parallel.

The trading partners themselves do not need to integrate with the tax authority directly. From the seller's and buyer's point of view, the e-invoicing experience is unchanged. The new responsibility lives with the certified Access Points.

Tax authorities want timely, structured visibility into B2B transactions to fight VAT fraud, accelerate refunds and reduce the administrative burden on businesses (in theory, by replacing periodic VAT returns with what they call "pre-filled" reports). The classic answer in countries like Italy or Brazil has been to route invoices through a central government portal: every invoice passes through a state-run system before reaching the buyer.

The five-corner model is the European alternative. Instead of building a central portal and forcing every business to integrate with it, it reuses the Peppol delivery infrastructure that is already in place and adds a reporting flow on top. Trading partners stay on the network they already use; the tax authority becomes one more endpoint that the Access Points talk to.

This is the architecture that Belgium has chosen for its 2028 e-reporting layer. France has chosen a closely related architecture through PDPs and a central portal. Both approaches preserve the four-corner core. The EU's VAT in the Digital Age (ViDA) reform will require near real-time digital reporting for cross-border B2B transactions across all member states by 2030, and is broadly compatible with the five-corner approach.

In most cases the migration from four corners to five is transparent for the seller and the buyer. The Access Point handles the reporting flow; the seller's ERP keeps producing invoices the same way; the buyer's system keeps receiving them. What does change in practice is that data quality matters more. If a business term is missing or wrong, the tax authority sees it immediately, not three months later when the periodic return is filed.

That makes pre-flight validation essential. Running every outgoing invoice through a Peppol BIS 3.0 validator before it reaches the network catches the schematron failures that would otherwise show up as a rejection or a tax-side correction request. The Peppol Validator on this site does exactly that, for free, with no signup.