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.

7 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

   Business terms, the totals ladder that has to reconcile exactly, and the VAT breakdown that is not one number.

5. 05

   Validation

   Three layers in order, what the eleven hundred rules actually consist of, and how to test against a release before it is mandatory.

6. 06

   Sending and receiving

   Getting a document onto the network through somebody else's Access Point, what that costs, and what receiving obliges you to do.

7. 07

   Building it: Laravel and Go

   The three parts of an integration: a writer, a validator in CI, a lookup, and the schema changes that have to come first.

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