NASIT s.r.o.

e-Invoicing, without the guesswork.

An API that turns your invoice data into valid e-invoices, checks them against EN 16931 before they go out, and tracks what happened after they were sent.

Talk to usSee what we build

EN 16931 · UBL 2.1 · hosted in the EU

POSTapi.nasit.sk/v1/invoices
{
  "issueDate": "2026-08-21",
  "currency": "EUR",
  "supplier": {
    "name": "Acme s.r.o.",
    "vatId": "SK2020123456"
  },
  "lines": [
    {
      "description": "Consulting",
      "quantity": 12,
      "unitPrice": 85.00
    }
  ]
}
INV-2026-0418accepted
  1. Document builtUBL 2.1
  2. ValidatedEN 16931 · 0 errors
  3. Sent240 ms
  4. Accepteddelivered

Based in Slovakia

A registered s.r.o., working with clients across the EU and invoicing in EUR.

A small team

You talk to the people writing the code. No account managers in between.

Standards first

We build on EN 16931 and UBL 2.1 rather than on a single vendor's format.

When Peppol becomes mandatory

Slovak e-invoicing is not a proposal any more — it is law, with a date attached. Here is how it got here and what is still ahead.

Apr 2025

The EU clears the way

VAT in the Digital Age is adopted as Directive (EU) 2025/516 and enters into force. Member states no longer need a derogation from Brussels to make domestic e-invoicing compulsory, which is what unblocks everything below.

Dec 2025

Slovakia writes it into law

Law 385/2025 Z.z. amends the VAT Act. The model is decided: a decentralised Peppol five-corner network, invoices as EN 16931 XML in UBL 2.1 or CII, and accredited providers — the digitálny poštár — carrying the documents. The Financial Directorate becomes the Slovak Peppol Authority.

2026

The voluntary window

You are here

The list of accredited delivery providers went out in March and the test environment opened in the second quarter. Nothing is enforced yet, which makes this the cheapest time to discover that your invoice data is missing unit codes.

Jan 2027

Peppol becomes mandatory

Domestic B2B and B2G invoices must be structured EN 16931 XML sent over Peppol, with supplier data reported to the Financial Administration in near real time. A PDF stops being a valid invoice for anything in scope. A penalty-free run-in until 31 March 2027 has been proposed but is not final yet.

Jul 2030

Cross-border joins in

The EU digital reporting requirements take over intra-EU B2B trade, buyer-side reporting starts, and the VAT control statement and EC sales list are retired. Invoices have to be issued within ten days of the supply.

Jan 2035

Everything converges

Member states that had their own clearance systems before 2024 must align them with the EU standard. From then on it is one format across the union rather than one per country.

Dates as published by the Financial Administration and the European Commission, current as of August 2026. The detail around the 2027 start is still being amended, so treat this as orientation rather than as tax advice.

What we build

Three products that share one data model. Take the whole set or only the piece you are missing.

NASIT Invoice API

Invoice data in, valid documents out

Post an invoice as JSON and get back a UBL 2.1 document that conforms to EN 16931, plus a stable reference you can store next to your own record.

  • REST API
  • Webhooks
  • Idempotent writes

NASIT Validator

Catch the errors before your customer does

Schema and business rules evaluated in milliseconds, with plain-language messages that point at the field that is wrong instead of a rule code.

  • EN 16931 rules
  • Readable errors
  • Runs in your CI

NASIT Connect

Delivery and status, in one place

Send documents through the channel your counterparty uses and keep the full history of every state change, so nobody has to log into a portal to check.

  • Delivery tracking
  • Document archive
  • Audit history

The unglamorous details

Invoicing is mostly edge cases. These are the ones we have already handled so your team does not have to.

UBL 2.1 and EN 16931

We work from the European standard, so the same mapping keeps working when the rules around it change.

Submissions stay idempotent

Retry a request as often as you like. A network timeout will not produce a second copy of the same invoice.

Status you can subscribe to

Signed webhooks for validated, sent, accepted and rejected, plus an endpoint for the days you need to backfill.

Errors written for humans

Validation output names the field and the line it belongs to, in a sentence you can forward to your accountant.

Documents kept and exportable

The original XML and every state transition are stored and can be exported in bulk whenever you ask.

Hosted in the EU

Infrastructure and backups stay inside the European Union. Self-hosting is possible if your policy requires it.

Questions we get asked

If yours is not here, write to us and you will get an answer from someone who has actually built the integration.

Let's look at your invoices together

Send us a handful of your real documents. We will run them through the validator and come back with what would be rejected, roughly what it takes to fix, and whether we are the right people for the job. No slide deck required.

hello@nasit.sk

NASIT s.r.o. · Slovakia · working with clients across the EU

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