Mandatory e invoicing in 2028: are your ERP, accounting software and internal app ready?

From 1 January 2028, businesses will exchange structured e invoices exclusively for mutual supplies of goods and services carried out in Slovenia. This is not just a change to an email attachment. The key question is whether your ERP, accounting software, online shop or internal application can create, send, receive and correctly process the required data.

What changes on 1 January 2028?

The Act on the Exchange of Electronic Invoices and Other Electronic Documents, known as ZIERDED, mandates the exchange of e invoices between business entities for mutual supplies of goods and services carried out in Slovenia. This covers business entities registered in the Slovenian Business Register and sole traders.

Different rules apply to consumer invoices and cross border business. The act also does not mean every company must build a new system or replace its accounting software. It does mean that the actual invoice pathway must be able to process a structured document through one of the permitted electronic channels.

The official explanation of the change is published by the Ministry of Finance, and the full requirements are set out in the published text of ZIERDED .

A PDF invoice and a structured e invoice are not the same thing

A PDF is intended mainly for a person: we open it, read it and print it. The data inside it are not necessarily written so that another information system can reliably interpret them automatically. A PDF on its own is therefore not a structured e invoice under ZIERDED.

A structured e invoice is a machine readable data document. Individual data items have a defined place and meaning: issuer, recipient, line items, taxes, amounts, dates and references. The recipient's system can check and process them without manual retyping.

The act envisages e SLOG, syntaxes compliant with the European standard, and other internationally established standards where this has been previously agreed in the contractual relationship between issuer and recipient. A human friendly display can still be added, but the essence of the e invoice is structured content.

An e invoice is a data flow, not a standalone file

In an orderly process the invoice travels through several connected steps:

1. Sales, an online shop or an internal application record the order or the service performed.
2. The ERP or accounting software prepares the invoice data.
3. The system checks mandatory fields, amounts, tax data and the recipient.
4. The invoice is converted into a supported structured standard and sent via the chosen e channel.
5. A delivery receipt message is automatically exchanged via the e channel, and exchanging a content confirmation or rejection is also possible.
6. The status is written back into the system the team uses every day.
7. The issuer and recipient ensure the e invoice is retained in line with tax and accounting regulations.

The biggest problems are often not in creating the file, but between systems. If a customer's tax number differs between the CRM and the accounting software, or an internal application never receives a rejection status, staff still end up checking and retyping data manually. It is therefore worth reviewing the entire integrations and data flows, not just the invoice issuing button.

Which channels will be available for exchanging e invoices?

For exchanges between businesses, ordinary email will not be a permitted channel for an e invoice. The document will have to travel via an e channel provider, the PEPPOL network or a certified access point, or via an agreed direct connection between information systems.

E channel provider

A company will be able to use an e channel provider listed in the register maintained by UJP. The list of providers is established on 1 October 2027. The provider handles secure transfer, routing of the document and, where needed, conversion between standards. Before choosing, check supported formats, integration options, return statuses, price and liability in the event of an error.

The PEPPOL network

Exchange will also be possible via the PEPPOL network or certified access points. This is particularly relevant for companies already operating in the wider European environment or using systems with existing PEPPOL support.

Direct connection between systems

Business partners can agree on a direct exchange between their information systems if they meet the required conditions. This approach makes sense mainly for a high volume of documents or closely linked partners, since it requires reliable identification, security, delivery and return messages. Even with a direct connection, ZIERDED requires the business entity to have at least one chosen e channel provider.

A free application for simpler cases

For entities with a smaller number of transactions or with simple or repetitive transactions, the act envisages a free application provided by the tax authority. Exchange takes place via UJP as a single entry and exit point, which in this case performs the tasks of an e channel provider. For a smaller company this may well be enough. If data already arise in several systems, however, additional manual entry into a new application can preserve the exact problem you want to eliminate.

This does not mean reporting every exchanged e invoice to FURS. ZIERDED also does not change the rules on tax verification of cash invoices.

How to check whether your system is ready

A provider's answer that "e invoices will be supported" does not yet tell you how the feature will work in your process. Check the following:

• Where does the first data point arise: in the shop, CRM, service application, ERP or on paper?
• Which program is the primary source of data on customers, items, prices and tax settings?
• Which standard can the system create, and which can it receive?
• Does the program have an API, structured import or export, and how does it return statuses?
• What happens when a mandatory data item is missing or the invoice is rejected?
• Who in the company sees the error and who is responsible for the fix?
• How do confirmation, posting, the audit trail and retention work?

With your software provider, check specific support for e SLOG or another agreed standard, the method of connecting to the e channel, return messages, handling of rejections, and the requirements of your version or licence. A general statement of "we support e invoices" without these answers is not enough to plan the whole process.

Checklist for preparation before 2028

• List all the programs in which data for issued invoices arise.
• List where received invoices arrive today and who confirms them.
• Map the path from order or service to posting and payment.
• Flag every manual retype, Excel export and attachment sent by email.
• Determine the primary source of data on customers, products and prices.
• Check with your software provider which standards are supported and the upgrade plan.
• Check the API, import, export, return statuses and error handling.
• Assign a person responsible for rejected or technically failed invoices.
• Check user rights, change history and retention.
• Run a test from invoice creation through to receipt, posting and return status.

Do you have to replace your ERP or accounting software?

As a rule, no. A small company with a single modern accounting program may only need a provider upgrade or the free application. A company with an ERP and an internal application needs to check whether the systems exchange all data and return statuses. An online shop or a B2B portal needs to reconcile the order, customer, stock, payment and invoice.

If orders are already manually retyped into the ERP today, support for a new format on its own will not eliminate the duplication. A sensible solution is often to connect existing systems, not to replace them completely. The page how a project runs shows how an inventory turns into a workable first scope.

Prepare the whole process, not just the file

2028 is far enough away that the process can be sorted without panic, and close enough that preparation should not be left to the last upgrade. First establish where data arise, who confirms them, which system issues the invoice and where statuses come back. Only then choose the e channel and the technical solution.

Related reading: B2B ordering portal and examples of automation in small companies.

This article is informational and does not replace legal, tax or accounting advice. Before implementation, check the applicable legislation, implementing regulations and your provider's instructions.