E-Invoicing in Practice: What It Is and When It Becomes Mandatory

What is an e-invoice — and what isn't?

An e-invoice is not a PDF sent by email. This is the most common misconception — a PDF is a digital image of a document, which a computer cannot automatically read and post without manual input. An e-invoice is a structured electronic document (typically XML) that an information system receives, processes, and posts without human intervention.

The practical difference: a PDF requires an accountant to manually enter data into the system. An e-invoice goes into the system automatically — no typing, no errors, no delay. In countries where e-invoicing is mandatory for the public sector (Slovenia, Croatia, most of the EU), suppliers to public contracts must submit invoices in a machine-readable format.

When is e-invoicing legally mandatory in the EU?

EU Directive 2014/55/EU made e-invoicing mandatory for all suppliers to contracting authorities (government bodies, municipalities, public institutions) across the EU. The deadline for compliance passed in 2019. Each member state implemented the directive with a national standard — in Slovenia this is e-SLOG 2.0, in Croatia UBL, and the cross-border standard is the European norm EN 16931 (also accessible via the Peppol network).

For B2B transactions between private companies, e-invoicing is currently mandatory in Italy, Spain, and France. The EU's VAT in the Digital Age (ViDA) initiative aims to extend mandatory B2B e-invoicing across all member states by 2028.

Which e-invoice formats should you know?

For EU cross-border business: Peppol BIS (Business Interoperability Specifications) — a common format for e-invoice exchange between EU countries. For national public sector invoicing: your country's national standard (e-SLOG in Slovenia, eRačun in Croatia). For B2B across the EU post-2028: EN 16931.

In practice, you don't need to know these formats — your accounting software does. When choosing software, verify that it supports your national format and Peppol. Systems that don't support these can't help you with public sector invoicing.

How to simplify e-invoice submission to the public sector?

Manual submission of each e-invoice to a public sector buyer involves: creating the invoice in your system, exporting to the required format, logging into the submission portal, uploading the file, and confirming. For 5 invoices per month, this is manageable. For 50, it's time-consuming.

Integrating your invoicing system with the public sector API simplifies this to one step: create the invoice in your system, and it is automatically transmitted. No manual export, no file upload, no format checking.

What are the benefits of e-invoicing for B2B?

Even where e-invoicing isn't mandatory, the benefits are clear. Time: automated import of an e-invoice into an accounting system eliminates manual data entry, which takes an average of 10–15 minutes per invoice. For a company receiving 100 invoices per month, that's 1,000–1,500 minutes — 17–25 hours of administrative work.

Errors: manual data entry generates transcription errors (wrong tax number, wrong amount, wrong date). E-invoices processed without human intervention eliminate these errors entirely.

How to get started with e-invoicing without technical expertise?

Step 1: check whether your accounting system supports your national e-invoice format and Peppol. If not, it's time for an upgrade.

Step 2: register with the relevant national e-invoice platform for public sector submission — this typically takes 1–2 business days and is free.

Step 3: configure the integration between your system and the submission platform (a one-time setup done by your software provider). After that, every public sector e-invoice is automatic.