The guide

Peppol for API Developers

Eight chapters on the parts of e-invoicing that matter when you are the one writing the code. Free, readable on the web, and written for developers rather than finance teams.

3 of the 8 chapters are written. The rest follow before the UK publishes its e-invoicing roadmap at the Budget on 28 October 2026, and chapter 8 is updated the same day.

In the meantime the reference is complete: the developer docs, every one of the 1,103 validation rules, and the API reference.

Contents

1. 01

   E-invoicing, and why the UK is moving

   What separates an e-invoice from a PDF, where the UK actually stands, and why the deadline matters before 2029.

2. 02

   How Peppol works: the four-corner model

   Sender, sender's Access Point, receiver's Access Point, receiver — and the lookup that makes addressing work at all.

3. 03

   Participant identifiers

   A scheme and a value, the UK codes that matter, and why the same company can exist twice on the network.

4. 04

   The invoice itself

   EN 16931 as the European semantic model, Peppol BIS Billing 3.0 as the profile that constrains it, and UBL 2.1 as the syntax. Business terms (BT-) and groups (BG-), and how they map to the XML you have to produce.

   Not written yet

5. 05

   Validation

   The three layers, in order: the UBL schema, the EN 16931 rules, then the Peppol rules. Why a document that passes one can still fail the next, what the twice-yearly rule releases change, and how to test against a release before it is mandatory.

   Not written yet

6. 06

   Sending and receiving

   Getting a document onto the network through an Access Point's API without becoming one yourself: what a partner does for you, what it charges for, and what you still have to get right before handing a document over.

   Not written yet

7. 07

   Building it: Laravel and Go

   Putting it together in code: producing a document from your own data model, validating it in CI, looking a counterparty up before you send, and what to store when nothing may be stored.

   Not written yet

8. 08

   What we know about the UK mandate

   Every claim labelled confirmed, announced or speculative, with its source. Updated on Budget day, 28 October 2026, when the roadmap is published.

   Not written yet