Software Engineer III

Job Description: We are seeking a highly skilled Software Engineer with extensive experience in ACI Postilion Realtime SDK, payment network integrations, and transaction switching. The ideal candidate will be responsible for designing, developing, and supporting high-volume payment processing solutions that integrate with card networks, EFT networks, core banking systems, and third-party payment services. This role requires strong expertise in electronic payments, ISO 8583 messaging, transaction routing, authorization processing, network connectivity, and end-to-end payment transaction lifecycle management.

Key Responsibilities Postilion Development

Design, develop, and maintain custom applications using Postilion Realtime SDK. Develop new nodes using Rest API, routing logic, and authorization modules within the Postilion platform. Customize and support Postilion transaction workflows to meet business and network requirements. Develop interfaces between Postilion and external systems, including issuer hosts, fraud systems, and payment gateways. Participate in system enhancements, upgrades, and migrations.

Payment Network Integration

Design and implement integrations with payment networks, including: · Visa · Mastercard · Pulse · NYCE · STAR Support network certifications and transaction testing activities. Implement and troubleshoot network management messages and routing configurations. Analyze network specifications and translate them into technical solutions.

Transaction Processing & Switching

Configure and support ATM, POS, debit card, credit card, and digital payment transaction processing. Design and maintain authorization, stand-in processing, routing, settlement, and reconciliation functions. Investigate and resolve transaction failures and network communication issues. Optimize transaction performance and throughput for high-volume payment environments.

ISO 8583 & Messaging

Develop and troubleshoot ISO 8583 message parsing, transformation, and routing. Map transaction messages between payment networks and internal systems. Analyze message logs and perform transaction-level troubleshooting. Support custom message formats and network-specific extensions.

Production Support

Monitor production transaction flows and switch performance. Provide Level 2/Level 3 support for payment processing applications. Conduct root cause analysis and implement corrective actions for incidents. Participate in on-call support rotations and critical production deployments. Ensure system uptime, resilience, and regulatory compliance.

Security & Compliance

Support PCI DSS compliance initiatives. Implement secure transaction processing practices. Work with HSM integrations for PIN and key management. Ensure adherence to payment industry security standards.

Required Qualifications

Experience

5+ years of software development experience. 5+ years of hands-on experience with ACI Postilion. Strong experience developing solutions using Postilion Realtime SDK. Experience supporting production payment switching environments. Proven experience integrating payment networks and third-party processors.

Technical Skills

Strong understanding of ISO 8583 transaction messaging. Experience with: ATM transaction processing POS transaction processing Debit and credit card payment systems Authorization and settlement flows Programming experience in Java. Proficiency with SQL and relational databases. Strong TCP/IP networking knowledge. Experience with REST APIs, Web Services, and socket-based integrations. Familiarity with Windows and Linux server administration.

Network & Payments Expertise

Experience integrating with Visa, Mastercard, Pulse, NYCE, STAR, or similar networks. Knowledge of acquiring and issuing transaction flows. Understanding of network certification processes. Experience troubleshooting network connectivity and transaction routing issues. Familiarity with payment settlement and reconciliation processes.

Preferred Qualifications

Experience with Postilion Office, Postilion Portal, Postilion Office Recon product. Experience with HSMs such as Atalla AKB, Thales, or Entrust. Knowledge of EMV, contactless, tokenization, and digital wallets. Knowledge of Visa, Mastercard SMS, or similar payment processing platforms. Experience working in Agile/Scrum environments.

Desired Skills

Strong analytical and troubleshooting capabilities. Excellent verbal and written communication skills. Ability to work effectively in mission-critical production environments. Strong understanding of payment ecosystems and transaction processing. Ability to mentor junior engineers and lead technical initiatives. Self-motivated with a strong focus on quality and operational excellence. As a forward-thinking software provider, Computer Services, Inc. (CSI) helps community and regional financial institutions solve their customers’ needs through open and flexible technologies. In addition to its award-winning core banking platform, these include the latest in lending, digital banking, payments, financial crime prevention and cybersecurity. Building on its 60-year track record of personalized service, CSI is shaping the future of banking and empowering its customers to rival their competition. For more information about CSI, visit CSI provides rewarding and challenging career opportunities for our employees. When determining your pay, we consider various factors such as your skills, qualifications, experience and location. Along with a competitive salary, this position includes eligibility for incentive awards based on both individual and business performance. We also offer a comprehensive range of benefits. To learn more about our benefits, visit:

Benefits Summary CSI is an Equal Opportunity Employer. All qualified applicants will receive consideration for employment without regard to race, color, religion, sex, pregnancy, sexual orientation, gender identity, national origin, age, physical and mental disability, marital status, veteran status, or any other characteristic protected by applicable law. If you need an accommodation during the recruitment process, please email us at View email address on click.appcast.io and we will work with you to meet your accessibility needs. For applicants residing in California, please read Privacy Notice for California Residents | CSI (csiweb.com) Visa Sponsorship: We are unable to offer visa sponsorship for this position. Applicants must be authorized to work in the United States without the need for sponsorship now or in the future.