Software Engineer III
CSI
About the role
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 www.csiweb.com
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 recruiter@csiweb.com 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.
Responsibilities
- Develop and maintain applications using the Postilion Realtime SDK.
- Integrate payment networks, processors, and external systems.
- Configure and support payment transaction routing, authorization, settlement, and reconciliation.
- Troubleshoot ISO 8583 messaging and production transaction issues.
- Provide production support, root cause analysis, and participate in on-call rotations.
- Support payment security, PCI DSS compliance, and HSM integrations.
Qualifications
- 5+ years of software development experience and hands-on ACI Postilion experience.
- Experience developing with the Postilion Realtime SDK and supporting production payment switching environments.
- Experience integrating payment networks and third-party processors.
- Strong knowledge of ISO 8583, ATM and POS processing, and authorization and settlement flows.
- Java programming experience, SQL and relational database proficiency, and TCP/IP networking knowledge.
- Experience with REST APIs, web services, and socket-based integrations.
- Familiarity with Windows and Linux server administration.
- Ability to troubleshoot payment routing and network connectivity issues.
Benefits
- Comprehensive benefits package.
- Eligibility for incentive awards based on individual and business performance.
Skills mentioned
About CSI
As a forward-thinking financial technology and software partner, we help community and regional banks, as well as organizations worldwide, solve their customers’ needs through open and agile technologies. Create World-Class Customer Experiences Compete in today’s open banking environment and exceed customers’ expectations with a unified, seamless banking experience. Your bank can grow assets, develop additional revenue streams and reach new customers by integrating digital technologies—while taking advantage of trusted fintechs’ embedded capabilities. Simplify Your Loan Origination Empower your customers to apply for a loan anywhere, at any time, while simplifying consumer and commercial lending process with a purpose-built solution for community banks. Protect Your Institution’s Reputation and Ensure Compliance Minimize your risk of non-compliance penalties, protect your institution’s integrity and keep regulators satisfied by leveraging the latest tools. Safeguard Your Data, Systems and Users Protect your organization around the clock and rest assured that you’re covered, with unparalleled support for detecting and remediating threats in real time. Boost Your System Performance Don’t accept a one-size-fits-all approach for your IT strategy. A scalable, efficient and tailored IT enterprise supports your growth and regulatory needs, maximizing the health and performance of your key applications, systems, networks and users. Maintain Communications with Customers Whether your customers prefer traditional documents or digital statements, modern communication keeps you connected. Multi-channel document services simplify access to statements and notices, reduce costs, shorten delivery times and enable new cross-marketing opportunities. Mitigate Risk and Manage Your Business Goals Reduce your time and expense spent managing security and compliance while ensuring your technology is aligned to business objectives.