Java Developer – Peppol AS4 / E-Invoicing Integration

Role Overview

SRQ Companies is expanding its e-invoicing technology platform, Muhasib, with a focus on Peppol-based electronic invoicing and integration with ERP and accounting systems. We are looking for a strong Java Backend Developer to join our technology team and take responsibility for the development and integration of our Peppol AS4 messaging layer.

Responsibilities

• Develop and maintain Java-based components for Peppol AS4 messaging and e-invoicing.
• Integrate and customize established open-source AS4 implementations such as phase4.
• Work with Apache CXF, Apache WSS4J and XML Security where required.
• Implement and troubleshoot AS4 messaging, SOAP, WS-Security, XML Digital Signature, XML Encryption, RSA-OAEP, TLS, and digital certificates.
• Investigate interoperability issues between our AS4 implementation and Peppol Access Points / endpoints.
• Work with SMP/SML discovery, participant identifiers, and service metadata.
• Integrate the Java AS4 service with our existing PHP-based Muhasib platform through REST APIs.
• Develop reliable message handling including retries, error handling, logging, and duplicate detection.
• Work with XML-based invoice standards including UBL and Peppol BIS/PINT.
• Support integration testing with Peppol test environments and external Access Points.
• Maintain secure, scalable and production-ready backend services.

Requirements

• 3+ years of professional Java development experience.
• Strong knowledge of Java 11+ / Java 17+.
• Strong experience with Spring Boot / REST APIs.
• Good understanding of SOAP and web services.
• Strong knowledge of XML, XML namespaces, XSD and XML processing.
• Experience with digital certificates, keystores, TLS and public-key cryptography.
• Experience troubleshooting complex integration and interoperability issues.
• Experience with Git and standard software development practices.
• Bachelor's degree preferred.

Skills

• Java
• Spring Boot
• SOAP
• XML
• REST APIs