How to Send a Compliant E-Invoice Under New Tax Rules

The short version: a compliant e-invoice under the new tax rules is a structured data file (usually UBL or UN/CEFACT XML) sent through an approved network such as Peppol, KSeF or SDI, not a PDF attached to an email. If you're still emailing PDFs to customers in Poland, Germany, France or Italy, you are already out of step with what those countries now require, and in some cases your customer cannot legally reclaim the VAT on what you've sent them.

What a "compliant e-invoice" means now

For years, "e-invoicing" meant sending a PDF instead of a paper invoice by post. That is not what the new rules mean by the term, and this confusion is causing real problems for small businesses right now.

Under the new generation of tax rules, an e-invoice is a structured, machine-readable document, usually in UBL 2.1 or UN/CEFACT CII format, that a tax authority's system or your buyer's accounting software can read and validate automatically without a human opening it. A PDF is a picture of an invoice. A structured e-invoice is data. Tax authorities want the data, because it lets them cross-check VAT in something close to real time instead of waiting for a quarterly return.

This is the bit most articles skip over because it's not flattering to say out loud: this whole wave of reform is not really about making your life easier. It's about closing the VAT gap. The EU loses an estimated 89 billion euros a year in unpaid VAT, according to European Commission figures, and structured e-invoicing gives governments visibility into transactions the moment they happen. Small businesses are the ones footing the software bill for that visibility. That doesn't make it wrong to comply, but it's worth naming, because it explains why the rules keep getting stricter rather than simpler.

The rules that apply right now, country by country

There is no single "new e-invoicing law." It's a patchwork, and the deadlines have shifted more than once, so treat every date below as one to double-check with your accountant before you act on it.

• Germany: since 1 January 2025, every German B2B business has had to be able to receive structured e-invoices (XRechnung or ZUGFeRD format). Issuing them becomes mandatory for larger businesses from 2027, and for everyone by 2028.
• France: mandatory e-invoicing for domestic B2B transactions, run through the government's Portail Public de Facturation and certified private platforms, is rolling out from September 2026 for larger and mid-sized companies, with smaller businesses following in 2027.
• Poland: the KSeF national e-invoicing system becomes mandatory in stages through 2026, starting with the largest taxpayers. Invoices sent outside KSeF will not count for VAT purposes once the mandate applies to your business.
• Italy: has run mandatory e-invoicing through its SDI system since 2019, so if you're already trading with Italian businesses, you've likely dealt with this format already.
• UK: HMRC ran a consultation on e-invoicing in 2025 and is expected to push adoption of the Peppol network for domestic transactions, starting with voluntary use before any mandate. There is no UK legal requirement to send structured e-invoices yet, but if you sell into the EU, your buyer's rules apply to what they need to receive.

If any part of your business sells into or operates in these markets, the rule that matters is your customer's country, not yours. I have a UK client who assumed the French rules didn't touch her because she's based in Brighton. They do, because her biggest customer is a distributor in Lyon.

The Peppol network, and why it matters more than any single country's rule

Most of these national systems either run on, or are compatible with, the Peppol network (Pan-European Public Procurement Online), which now operates in more than 30 countries including Australia, Singapore and New Zealand, not just Europe. Peppol works like a postal system for structured invoices: you send your invoice to your own "access point" provider, which validates it against the required format and routes it to your customer's access point, which delivers it into their accounting system.

You don't need to understand the plumbing. You need an access point provider, which is usually built into modern accounting or invoicing software rather than something you set up separately. This is one area where cloud-based invoicing platforms earn their subscription fee, because building Peppol or KSeF connectivity yourself is not a weekend project.

How to send a compliant e-invoice: the step-by-step

Here's the process I walk clients through, whether they're a five-person agency or a manufacturer shipping into three EU countries.

1. Work out which rule applies to you. It's determined by where your customer is registered for VAT, not where you are. Make a simple list: customer, country, current invoice method, applicable e-invoicing deadline.
2. Check whether your existing software supports structured formats. Ask your provider directly: "Can you generate UBL 2.1 or XRechnung, and do you have a Peppol access point?" Many mid-tier tools (Xero, QuickBooks, Sage) have added this in the past 18 months but not all plans include it, so check your specific tier, not just the brand name.
3. Populate every mandatory field correctly, including the boring ones. The EN 16931 European standard requires more than 30 fields, including buyer and seller VAT numbers, a unique invoice reference, currency codes, and structured line items with tax categories per line, not just a total. A missing or malformed VAT number is the single most common reason a structured invoice bounces.
4. Get the address details exactly right. This sounds trivial next to VAT codes, but structured invoicing systems validate address fields programmatically, and a mismatch between the registered address and what's on the invoice causes automatic rejection in some national systems. I've written separately about why invoices need a proper address on them, and under these new systems it stops being a nice-to-have and becomes a hard validation rule.
5. Send through the network, not by email. Once a country's mandate applies to you, emailing a PDF, even a beautifully formatted one, does not satisfy the legal requirement. Your software should transmit the structured file through your access point automatically; you should never be manually attaching invoice files once this is set up.
6. Archive for the required retention period. Germany requires structured invoice archiving for 10 years. France and most EU states require at least six. Keep the original structured file, not a printed or PDF copy of it, because the structured version is the legal record.
7. Build a process for rejections and corrections. Structured systems reject invoices automatically if a field fails validation. You need a named person (not "someone on the team will notice") who checks for bounced invoices weekly, because an unpaid rejected invoice sitting unnoticed for a month is a cash flow problem you gave yourself.

A real example: the invoice that didn't exist as far as the tax office was concerned

A client of mine runs a small industrial parts business exporting from the Midlands into Poland and Germany, turnover around 1.8 million pounds. In early 2026, one of her Polish customers stopped paying an invoice that, as far as her team was concerned, had been sent, received and acknowledged by email three weeks earlier. It turned out the Polish buyer's finance team couldn't process it through KSeF because it had arrived as a PDF, and under their internal rules (ahead of the full national mandate, but already company policy), a PDF simply isn't a valid tax document anymore. To their accounting system, that invoice did not exist. Not "was queried." Did not exist.

The fix took about ten days: her invoicing software needed a plan upgrade to unlock the Peppol connector, someone had to manually re-key three months of outstanding invoices into the correct structured format, and she lost a full billing cycle of cash flow on that one customer while it got sorted. The lesson wasn't about Poland specifically. It was that "I emailed it, so it's sent" is no longer a safe assumption anywhere she trades, and she now checks every new customer's country requirements before onboarding them, not after the first invoice bounces.

Where AI helps, and where it doesn't

There's a lot of noise right now about AI "handling compliance for you," and some of it is fair. AI tools inside modern invoicing platforms can flag a malformed VAT number, auto-populate line-item tax categories from past invoices, and catch an address mismatch before you hit send, which cuts down the manual re-keying that ate my client's ten days. If you run a service business, I've written about this in more detail in how agencies are using AI for invoicing and admin.

What AI won't do is decide which country's rule applies to you, or fix a wrong VAT number, or absorb the legal responsibility if you send a non-compliant invoice anyway. That responsibility sits with you and your accountant. If you're choosing new software or a consultant to help set this up, it's worth running any vendor through a proper checklist rather than trusting the sales page, and my AI vendor evaluation checklist covers the questions to ask before you sign anything.

If your invoicing setup spans multiple countries and you don't have the internal capacity to map it, this is one of the areas where a short piece of paid help from someone who's done it before, an AI implementation coach, pays for itself in avoided rejected invoices alone. I'd rather see a business spend a few hundred pounds getting the setup right once than lose a billing cycle the way my Midlands client did.

The mistakes I see most often

• Assuming your accounting software "does e-invoicing" because it exports a PDF nicely. Ask specifically about UBL, CII, XRechnung or Peppol support, by name.
• Treating this as an IT problem, not a finance one. The rules are tax rules. Your accountant or bookkeeper needs to sign off on the field mapping, not just the software team.
• Waiting for the mandate date in your own country. If your customer is in a country where the rule already applies to them, the deadline that matters is theirs, not yours.
• Not archiving the structured file. A screenshot or printed copy of an XML invoice is not a valid archive copy under most of these rules.
• Assuming your accountant already knows all this. Plenty of good accountants are still catching up on the country-specific detail, particularly for smaller firms who don't have many EU clients yet. Ask directly rather than assuming it's covered.

None of this is glamorous work, but neither is losing a month's cash flow because an invoice technically didn't exist. Get the structured format right once, and it runs quietly in the background from then on.

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Frequently asked questions

Is a PDF invoice ever compliant under the new e-invoicing rules?

No, not once a mandate applies to your transaction. A PDF is a document image, not structured data, and most of the new systems (KSeF in Poland, SDI in Italy, the French national platform) will reject or simply not recognise a PDF as a valid tax invoice, even if your customer opens and pays it.

Do UK businesses need to send structured e-invoices right now?

Not yet under UK domestic law, HMRC is still consulting on adoption, likely centred on the Peppol network. But if you invoice customers in Germany, France, Poland or Italy, their national rules apply to what they need to receive, regardless of where you're based.

What software supports compliant e-invoicing?

Most major cloud accounting platforms including Xero, QuickBooks and Sage have added or are adding structured e-invoicing and Peppol connectivity, but support often varies by plan tier and country, so confirm with your specific provider rather than assuming your current subscription includes it.

What happens if I send a non-compliant invoice by mistake?

Consequences vary by country. In France, penalties can run up to 15 euros per invoice, capped annually. In Poland, once KSeF is mandatory for your business, an invoice sent outside the system generally won't count for VAT purposes at all, which can block your customer's ability to reclaim VAT on it. Check the specific penalty regime for each country you trade in rather than assuming they're all the same.