Nexo Retailer V5

Why we selected Nexo

At Worldline, we are committed to advancing open, future-proof payment ecosystems. As an active member of the Nexo Standards association , we chose to adopt Nexo Retailer V5 as the foundation for our Terminal API to make the integration process as seamless and painless as possible, empowering businesses to effortlessly enhance their payment capabilities and customer experiences.

The key reasons for this decision include:

• Global interoperability: Nexo Retailer is designed for international scalability and consistency across markets and acquirers.

• Paving the way for future-proof integrations: By aligning with Nexo Standards — a movement supported by many of Europe’s leading payment providers and terminal manufacturers — we’re helping to shape a more open, interoperable future in payment acceptance.

• Focus on innovation over reinvention: Leveraging a mature, community-driven standard lets us focus on enhancing capabilities — not duplicating efforts.

Instead of reinventing the wheel, we chose to accelerate innovation by building on a proven foundation — making it easier for our clients to integrate, scale, and stay ahead.

What is Nexo Retailer V5?

Nexo Retailer V5 is an open communication protocol that enables seamless, real-time interaction between a merchant’s Point-of-Sale (POS) system and a payment terminal. It is part of the suite of standards defined by Nexo Standards , a not-for-profit association aiming to bring global interoperability to the payments ecosystem.

Nexo Retailer is specifically focused on the Retailer-to-Acquirer interface — standardizing how POS systems send requests (like payments, refunds, or reconciliations) and receive responses from payment terminals. It supports use cases from traditional POS terminals to self-service kiosks and headless checkout systems.

Rather than relying on fragmented, proprietary protocols or custom middleware, Nexo Retailer V5 provides a transparent, hardware-agnostic, and internationally standardized approach to payment terminal integration.

Understanding the protocol

This section focuses on the high-level concept, while detailed implementation guidance — including sample messages, request/response flows, and error handling — is provided in the Build your integration section .

Terminal API uses Nexo Retailer V5 as its messaging backbone. This protocol defines the structure and behavior of messages such as:

All messages follow a predictable XML structure based on Nexo’s data model, which draws on ISO 20022 principles — enabling structured, consistent parsing and validation across systems. While Nexo itself defines XML message structures, the Terminal API transmits those messages wrapped in JSON over REST endpoints.

Compatibility with other Nexo Retailer integrations

The Terminal API implementation adheres to the official Nexo Retailer V5 specification, making it easy for developers with Nexo experience to integrate without needing to relearn core concepts or message structures.

Message formats, flows, and terminology remain consistent with the standard, ensuring a familiar development experience.

Where additional functionality is required, protocol extensions are applied in a structured and non-breaking way — primarily to support enhanced terminal features or value-added services. These extensions are fully documented.

The result is a standards-compliant integration experience, strengthened by Worldline’s ongoing contributions and technical leadership within the Nexo community.