From the 4-corner model to the Slovak 5-corner model

Peppol is often described as an invoicing network. In reality, it is a sophisticated technical infrastructure that allows systems from different companies to understand each other, regardless of the country or software used.
The basis of operation is the so-called 4-corner model. In this model, companies do not communicate with each other directly. Each company is connected to its own provider, the so-called Access Point, which ensures the sending and receiving of documents.

In practice, it works simply. The company issues an invoice in its ERP system and sends it to its Access Point. The latter checks the document for correctness, finds the recipient’s address via the Peppol directory, and then delivers the invoice to the other party’s Access Point. From there, it goes directly to the recipient’s system. The entire process is automatic without manual intervention.
Standardization is an important part. Invoices are not sent as PDFs, but as structured XML according to the EN16931 standard, most often in Peppol BIS format. Before sending, the document undergoes validation, which significantly reduces the number of errors.

In Slovakia, this model is being expanded with another element, creating the so-called 5-corner model. The Financial Administration also enters the process. The invoice is thus sent not only to the business partner, but also to the state.
After the invoice is issued and sent to the Access Point, which in Slovakia is known as the Digital Postman, the document is also sent to the Financial Administration system. Only then does it proceed to the recipient. Status reports on delivery and processing are generated throughout the process.
This approach increases control over VAT and brings greater transparency. However, it also places greater demands on integration. Companies must ensure the correct data format, partner identification, and connection to the service provider.

Modern solutions significantly simplify these steps. They automatically transform data into XML format, ensure validation and communication with the Peppol network and state systems.
From the perspective of businesses, the most important thing today is not to start solving this change at the last minute. We recommend analyzing your existing system now and finding out if it can export invoices and in what format. If it does not have this functionality, it is advisable to contact the system supplier and check the possibilities of expansion. Alternatively, consider a system that already supports e-invoicing and standards such as Peppol.

It is also a good idea to use the time until next year to select a suitable partner. Whether it is the Digital Postman in Slovakia or a provider that is already accredited today or in the process of accreditation, early selection will significantly simplify implementation. The list is available on the website of the Financial Administration of SK.

For companies that already use high-quality and modern systems today, not much will change in the end. The process will remain very similar, but the difference will be in the quality of the data. It will be more accurate, more consistent, and ready for automated processing without manual intervention.
In conclusion, Peppol is changing from a communication network to a regulated infrastructure. The Slovak 5-corner model is part of a broader trend in Europe where the state plays an active role in the processing of electronic invoices. Companies that prepare in time will gain an advantage and avoid unnecessary pressure just before the implementation of the obligations.