Starting January 1, 2027, mandatory electronic invoicing will begin in Slovakia for legally defined domestic transactions. For accountants, this changes more than just how invoices are delivered. The new regime will also affect how they are issued, received into accounting systems, verified, corrected, and archived.
In-house accountants therefore need to verify whether their current system can handle e-invoices and how it will connect to a digital postman. External accountants and accounting firms must also resolve access and document processing for individual clients. In all cases, it is necessary to know what happens with erroneous invoices, how attachments will work, and how document management will function overall.
An e-invoice is not a PDF. The accounting system works directly with its data
An electronic invoice will be a structured electronic document compliant with the European standard EN 16931. For electronic invoicing in Slovakia, the structured formats UBL 2.1 and CII (a widely used XML format) are used, which can be automatically processed by an accounting or enterprise system.
A PDF sent via email does not meet this requirement. It can continue to serve as a readable visualization of the invoice, but it is not an e-invoice itself. An e-invoice is a structured electronic document containing the data necessary for automated processing. A PDF visualization can be attached to an e-invoice, but sending it along with the XML is not mandatory and depends on settings or agreements between the parties involved.
For accountants, this change is significant primarily when receiving documents. It is no longer necessary to extract data from PDFs by retyping or using OCR. If the system is properly prepared, it works directly with structured invoice data. However, for this data to get from the issuer to the recipient, another link enters the process – a digital postman.
The digital postman ensures delivery, and processing continues in the accounting system
E-invoices will be delivered via the Peppol network and certified delivery service providers – digital postmen, which also include GRiT. At the same time, the electronic invoicing system also involves Financial Administration of the Slovak Republic, which will receive selected data from e-invoices and use it for tax administration purposes.
The digital postman ensures secure document transmission, technical checks, and communication within the Peppol network, including the transfer of required data to the Financial Administration. The received invoice must then be integrated into the company's accounting or approval process. Conversely, for issued invoices, it is necessary to provide the digital postman with the correct data and subsequently work with status information regarding delivery, data transfer to the Financial Administration, or any processing errors.
A new accounting system is not automatically required
The first step is not to replace your current accounting or ERP system, but to verify its readiness. Check with your system provider to see if it will be able to issue and receive e-invoices and communicate with the digital postman.
If it does not support the necessary formats or direct communication with Peppol, it does not necessarily mean it must be replaced. You can use an integration solution that takes data in its current format, performs the necessary validation and conversion, and handles communication with the digital postman.
This is how the solution from GRiT works. It can be connected to an existing ERP or accounting system and, depending on the specific scenario, take over conversion, validation, communication via Peppol, status information, and technical error handling. This allows a company to keep the system it currently uses and only add the components necessary for e-invoicing.
Attachments to e-invoices are still possible
The structured format of an invoice does not mean that related documents disappear from the process. In Peppol, you can attach documents such as delivery notes, timesheets, handover protocols, itemized breakdowns, contracts, or other supporting documents to an e-invoice. Supported formats include PDF, JPG/PNG, XLSX/ODS, and CSV.
For larger attachments, check the limits of your digital postman.
What happens if an e-invoice is incorrect
If an invoice fails to meet Peppol's technical or validation rules before being sent, the postman may reject it or return an error message. The sender then corrects it before successful delivery.
If the invoice has already been delivered but contains a factual error, such as an incorrect price, VAT rate, quantity, or recipient, the correction is handled between the supplier and the customer just as it is today. The original document cannot simply be overwritten or deleted. A credit note or correction document is issued for the original invoice, clearly referencing it.
What if a business partner does not yet use e-invoicing
In 2026, when participation in the Slovak system is voluntary, you will not be able to deliver an e-invoice via the network to a business partner who is not yet registered in Peppol. You will therefore send the invoice to them in the usual way, for example, as a PDF via email.
From January 1, 2027, entities subject to the obligation will be required to be capable of receiving e-invoices.
Accounting firms must manage multi-client workflows
For an accounting firm, simply setting up a technical connection for e-invoicing is not enough. Each client is a separate entity with its own identification, registration, and permissions, and their documents must remain strictly separated. At the same time, an accounting firm needs to manage invoices for multiple clients clearly from a single location, without mixing their data or access rights.
The solution should therefore support multi-client management.
When choosing a provider, the price per processed invoice shouldn't be the only deciding factor. It is also important to consider how the solution handles multiple companies, different accounting systems, and user roles, how it clarifies error states, what its security level is, and how it supports archiving or transferring documents to an archive in compliance with legal requirements.
How do I find out if my client already has a digital postman
Each company chooses its own digital postman from the certified providers listed on the Financial Administration website. You cannot simply find this out from the public list of providers. Therefore, the accounting firm must verify this information directly with the client.
GRiT connects e-invoicing with your accounting process
GRiT is a certified delivery service provider for Slovak electronic invoicing. We have also been dedicated to the electronic exchange of business documents and the integration of corporate systems for over 25 years.
We handle e-invoicing as a secure and reliable connection to your existing accounting and ERP systems. We offer both cloud and on-premise solutions, and thanks to our experience with electronic invoicing in Poland, Germany, Italy, Hungary, and other countries, we know how to deal with various legislative and technical requirements.
If you are looking for the ideal digital mail carrier for your business, schedule a consultation with us. GRiT will help you set up a solution tailored to your processes, systems, and document volume so that you are ready before January 1, 2027.
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