How We Built a Unified E-invoicing API for 31 Countries

Why multi-country e-invoicing is so hard

E-invoicing mandates across Europe have been accelerating, and 2026 is the year they cluster. Belgium went live on 1 January 2026. Poland’s KSeF mandate started for large taxpayers on 1 February 2026. France’s business-to-business mandate arrives on 1 September 2026. Each one chases the same goal — closing the VAT gap — and each one does it differently.

On paper, “send a compliant electronic invoice” is one task. In practice it is dozens of tasks sharing a name.

Every mandate brings its own format, its own submission protocol, and its own error-handling model:

• Germany uses XRechnung and the hybrid ZUGFeRD, both built on the EN 16931 standard.
• Italy uses FatturaPA, cleared through the Sistema di Interscambio (SdI).
• Poland uses the FA(3) structured XML schema, issued exclusively through the government’s KSeF platform.
• France accepts Factur-X, UBL, and CII, routed through certified private platforms (PDPs) and the public portal under its “Y-model.”
• Belgium requires structured invoices over the Peppol e-invoicing network, following EN 16931.

The format is only the surface. Beneath it sit different transport methods, different authentication schemes, different validation rules, and the part that quietly eats engineering time: different ways of telling you something went wrong. A rejection from KSeF looks nothing like a rejection from SdI, which looks nothing like a Peppol message-level response. Build for one country and you have built for exactly one country.

Why we turned it into a product

At Taxually, we built a lot of this e-invoicing compliance infrastructure for our own clients. Country by country, we wrote the adapters, mapped the fields, handled the rejections, and tracked the timeline changes that regulators publish on what can feel like a monthly basis.

A pattern kept showing up. The underlying job — connecting a billing system to a government-mandated e-invoicing network — was the same job for every developer and every finance team hitting these mandates. Everyone was rebuilding the same plumbing. The country-specific detail was real, but it was detail that could live behind a consistent interface instead of in everyone’s codebase.

So we packaged it.

What Clearvo does

Clearvo is a standalone e-invoicing API that puts 31 countries behind a single JSON endpoint. You send one structured invoice payload. Clearvo picks the correct format for the destination, validates it against that country’s rules, and submits it to the right network or government platform. It is the same call for Belgium as for Italy as for Singapore.

Here is what happens to a single payload:

1. You send one invoice. Describe it once, in a consistent structure, whatever the destination country.
2. Clearvo selects the format. It maps your payload to the right national format — Factur-X, FatturaPA, FA(3), Peppol BIS, and the rest.
3. Clearvo validates before it sends. It checks the invoice against the destination’s mandatory fields and business rules up front, so you catch errors in your own flow instead of days later as a platform rejection.
4. Clearvo submits to the right channel. It delivers to the correct destination, whether that is a clearance platform like KSeF (via the KSeF API) or SdI, or the Peppol network.

The differences between countries do not disappear — they cannot. They just stop living in your code.

The 2026 mandate wave, at a glance

If you are deciding what to build against first, the 2026 calendar is where the pressure sits. Here is how the three nearest European mandates compare:

The same wave is moving beyond Europe, through countries such as Singapore, Malaysia, and Saudi Arabia. That is exactly why one interface spanning 31 countries beats a single-country integration you have to repeat.

The current detail on each mandate — timelines, formats, and the fields each one requires — lives in the Clearvo country guides. If France’s September 2026 deadline is on your roadmap, the France e-invoicing checklist sets out what needs to be in place, and when.

What changes for your team

For a developer, a unified e-invoicing API turns “support a new country” from a project into a configuration change. You integrate the endpoint once and add destinations without rewriting your invoicing logic every time a regulator updates a schema or moves a deadline.

For a finance team, it removes the scramble that tends to land a quarter before each go-live. Entering a new market becomes a matter of switching a country on, not commissioning another build.

That was the pattern we kept seeing across our own clients. It is why we took the infrastructure we had already built and made it something any team can call directly.

See what your markets require

If you are weighing how to handle the 2026 mandates without a separate integration per country, the Clearvo country guides are the fastest way to see what each market needs — and how one API call covers all of them. Start at clearvo.io.

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