What is e-invoice?
Short answer
e-invoice is a structured electronic invoice in XML format based on the European standard EN 16931 and, in Slovak practice, Peppol BIS Billing 3.0. The receiving system can automatically read, validate and process its data without manual re-entry or OCR. A PDF or image sent by email is not an e-invoice merely because it is an electronic file; machine-processable structured data is decisive. The Slovak framework is set out in § 76a and § 85o of Act No. 222/2004 Z. z. on VAT. The mandatory B2B and B2G regime starts on 1 January 2027, while 2026 is a voluntary testing period.
4 things that make a document an e-invoice
XML as a core
A structured document according to the agreed standard, not just a visual form of the invoice.
Automation
The system can load individual fields without rewriting or OCR.
Control of rules
The document must pass both technical (XSD) and content validation (business rules EN 16931/Peppol).
Certified channel
Delivery takes place via a certified delivery service — e-invoicing delivery-service provider.
It is not the electronic format that matters, but machine readability
The right question is not whether an invoice was received electronically, but whether it can be processed by a machine. A PDF sent by email is an electronic file, but the system cannot reliably extract all the fields from it without OCR or manual intervention — and OCR commonly makes errors in amounts, dates or identifiers when processing invoices. An e-invoice should have structured fields (supplier, customer, dates, items, VAT, payment, identifiers) formatted so that they can be read by a computer, not a human. The key difference lies in Is a PDF invoice e-invoice? and What's the difference between PDF, XML and real e-invoice?.
The law, standard and network
Section 76a and Section 85o of the VAT Act
Act No. 222/2004 Coll. on VAT (as amended by Act No. 385/2025 Coll.) introduces the obligation and regulates the authenticity, integrity and legibility of the document. For further details, see which Act regulates e-invoicing.
EN 16931
A European technical standard defining mandatory and optional invoice fields — a common ‘language’ understood by systems across the EU.
Peppol BIS Billing 3.0
The specific technical implementation of the EN 16931 standard, which Slovakia uses in conjunction with the Peppol network. For details, see What is Peppol BIS Billing 3.0.
Peppol
A European delivery network through which invoices are transmitted between certified providers (e-invoicing delivery-service providers). More at what is Peppol.
The journey of a single invoice
XML is generated
From accounting/invoicing software or an online tool, in accordance with Peppol BIS Billing 3.0.
Check before shipping
Technical (XSD) and content (business rules) validation detects errors before the invoice is sent.
Via a e-invoicing delivery-service provider
A certified delivery-service provider sends the document via the Peppol network to the recipient’s post office.
Automatic import
The recipient automatically registers the document and, where applicable, posts it — without the need for manual transcription.
Depending on who you are
Find out if this obligation applies to you
Not everyone is obliged to issue invoices, but almost everyone will need to know how to accept them. See who is required to issue invoices and who is required to accept invoices.
Choose a e-invoicing delivery-service provider
You need a certified delivery-service provider — see how to choose one and how much it will cost.
Plan the process for your clients
Are you managing the selection and administration of couriers for several clients at once? — see Selecting a courier for multiple clients.
2026 voluntarily, 2027 mandatory
The year 2026 serves as a voluntary trial period — you can take part, test the processes and the e-invoice provider without incurring penalties for failing to meet the old deadlines. From 1 January 2027, e-invoicing becomes mandatory for domestic B2B and B2G transactions. The exact timetable, depending on whether you issue or only receive invoices, can be found in When do I have to start issuing e-invoices? and From when do I need to be able to receive them?.
What people wrongly believe
“An invoice sent electronically is automatically an e-invoice.”
No. It is the structure and machine-readability of the data that matter, not the method of delivery.
“A PDF with a QR code is enough.”
A QR code helps with payment, but it does not replace structured XML data.
“An e-invoice is just a technical matter for the IT department.”
It affects accounting, tax, archiving, relationships with partners and everyday business processes — not just technicians.
“If I only receive invoices, it doesn’t concern me.”
Almost every business will need to be able to handle e-invoices — see what if I only receive invoices.
Conclusion
An e-invoice is a data document that must be processable, validatable and traceable — not a visual invoice sent electronically. If you’re new to this topic, the next logical step is to find out whether the obligation applies to you, and then choose a e-invoicing delivery-service provider.
Verified sources
Act No. 222/2004 Coll. on VAT, Sections 76a and 85o (as amended by Act No. 385/2025 Coll.); EN 16931; OpenPeppol BIS Billing 3.0; Slovak Financial Administration — e-invoice: official methodological and information materials of the Slovak Financial Administration. Verified on 10 July 2026.
Official cases from the Slovak Financial Administration’s FAQs
The following questions and answers are taken from the current July FAQ from the Financial Administration and have been assigned to this topic. Grouping the cases prevents the creation of duplicate pages, whilst retaining the full answer and the exact wording of the question.
Example No. 1: What is e-invoice?
According to the European Directive, an electronic invoice is an invoice that has been issued, sent and received in a structured electronic XML format in accordance with the European standard EN 16931, in the UBL or CII standard, which an accounting programme can process automatically. Unlike standard PDF invoices or scanned (image-based) documents, an e-invoice contains structured data – that is, information recorded in such a way that a system can read and process it without manual transcription. This saves time and reduces the number of errors during data entry.
Primary source: Financial Administration of the Slovak Republic, FAQ 9/VAT/2025/IM k e-invoice, July 2026 update. Processed and checked on 13 July 2026.
Review of questions from an earlier presentation
The presentation by the Slovak Accountants’ Centre was used solely to identify practical issues. The following conclusion has been updated in line with a subsequent FAQ from the Financial Administration and the applicable legislation; we do not treat the author’s suggestions, recommendations or incorrectly merged fragments as legal rules.
- slide/page 5: What is the European standard for electronic invoicing?
- slide/page 6: Which European standard have we chosen in Slovakia?
Current conclusion: EN 16931 is the European semantic standard for e-invoicing, and UBL or CII are supported syntaxes. Peppol is a delivery network and a set of rules, not a substitute for the EN 16931 standard.
Primary sources: FAQ Financial Administration of the Slovak Republic k e-invoice, July 2026; Act No. 222/2004 Coll. on VAT Effective from 1. 1. 2027. Revised 13 July 2026.