> ## Documentation Index
> Fetch the complete documentation index at: https://strahinjamilosevic.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Adyen Terminal API reference

> OpenAPI for a non-REST payment protocol.

| | |
| - | - |
| Company | Adyen |
| Role | Technical Writer, in-person payments |
| Period | November 2021 – November 2024 |
| Result | A legacy, non-REST API published in the standard API Explorer without changing its protocol |
| Stack | OpenAPI, Python, nexo retailer protocol, API Explorer |
| Live site | [Terminal API in the API Explorer](https://docs.adyen.com/api-explorer/terminal-api/1/overview) |

## Why

The Terminal API is foundational to in-person payments. Its legacy structure made it hard to understand, maintain, and integrate with modern developer tooling. Making it accessible mattered for long-term platform scalability and developer trust.

## What

The Terminal API is a non-REST API based on the [nexo retailer protocol](https://www.nexo-standards.org/standards/nexo-retailer-protocol). For years, its only reference lived on a single page assembled from many HTML files. It was hard to navigate and incompatible with the OpenAPI-based API Explorer.

## How

I mapped the full API structure by reconciling the official nexo PDF specification, the existing documentation, and the OpenAPI requirements of the API Explorer tooling. I coordinated between the team that owned the Terminal API implementation and the platform team responsible for API reference pipelines.

We created a Python script that generates OpenAPI specs the tooling could consume. We introduced a new API Explorer page type that presents the API structure by request type.

## Result

The migration brought a critical legacy API into the standard developer experience without changing its underlying protocol. It reduced long-term maintenance risk and improved discoverability for a globally used payments API.

***

© 2026 Strahinja Milošević | Author of [all-maker.com](https://all-maker.com/), a part of the [tech writing blog webring](https://caseyrfsmith.github.io/webring/)


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