Peppol Plugged

WooCommerce API Integration with an EU wide eInvoicing system.

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The Project

NLeyes (a Dutch organisation that specialises in business optimisation and automation) came to me with a proposal. They were building an API that integrated with Peppol, a global eInvoicing system that would speed up procurement. In January 2026, some EU countries (Belgium, for example) introduced legislation that doing business with governmental systems would require invoices to be submitted to Peppol. NLeyes had written an API that generated a valid XML that could be submitted to Peppol – either through their API, or independently.

NLeyes were looking for an integration with the API for popular shopping services. I was brought on board to help develop the WooCommerce plugin, as I had previous experience with building plugins for commercial release.

What I Proposed

NLeyes would have both a free and premium option, so I proposed to make sure the codebase was stable and easy to maintain, I proposed we would build a free plugin that contained the majority of the functionality. The premium version would use WordPress hooks to hook into the free version. The free version would be used as a marketing tool for the project on WordPress.org, with upsells to the premium version.

What I Did

• Creation of an API interaction class that interacted with Peppol Plugged API.
• Adding functions to WooCommerce hooks that uses the API to submit to Peppol.
• A full debug suite to debug exactly what happens with the plugin when it fails.
• Extra hooks within the plugin to handle premium functionality.
• Coding to handle both XML and PDF receipts from the Peppol Plugged API.
• A creation of a system allowing the premium version to be updated using the standard WordPress upgrade process.
• Going through the plugin review system on behalf of the client.
• Making sure the plugin is translatable.
• Writing all documentation and further consulting on development and structure of the plugin.
• Setting up the plugin on Patchstack, so security vulnerabilities could be disclosed.

Challenges

The majority of challenges came from two sources.

The first was understanding the various tax systems that interact with Peppol. We began with focusing on the Dutch and Belgian tax systems, which are both different. Although both are similar and WooCommerce handles tax well, there were a couple of discrepancies which needed to be factored into the API.

The second issue was supporting WooCommerce. Once you release a plugin you could be asked for a number of different solutions. Although we decided early on with the minimum version of WordPress and WooCommerce we’d support, there were legacy carts and systems other clients had. We made sure the plugin was able to be run with legacy checkouts, and non HPOS supported sites, through rigourous testing. This would maximise the size of the

Results

By the end of the project, Peppol Plugged had the following:-

From the Client

Rhys was recommended to us by Jono Alderson, a former colleague of mine from our time at Yoast, and that recommendation proved spot on. He played a key role in the development of Peppol Plugged. Rhys works very independently, thinks along proactively, and took the time to truly understand the Peppol domain. He has all the knowledge and expertise required to build high-quality WordPress plugins. The collaboration with our developers was excellent, and the project turned out to be a great success. I can highly recommend working with Rhys.

Bob Breukhoven
Business Consultant, NLeyes