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CASE STUDY / FINTECH / BACKEND

Issuer Card Payment Processing Platform

Backend engineering contributions to an issuer card-processing platform, including API work, service integrations, database optimisation, and production support.

C# / .NETREST APIsSQL ServerPostgreSQLAWSJWT

Project context

A professional FinTech engagement supporting an issuer card payment processing platform. Work evolved from application development and production issue resolution to backend-focused engineering, integrations, and database performance.

Role 1 — Consultant Software Engineer

Focus: Legacy issuer card-processing application development and production support.

  • Built, enhanced, and maintained core modules in the legacy card-processing application.
  • Performed spike investigations to understand complex issues, identify root causes, and help resolve production-critical defects.
  • Contributed to the separate Cardholder Data Isolation Interface initiative; see its dedicated case study.

Role 2 — Consultant Senior Software Engineer

Focus: Backend engineering, API development, integrations, database performance, and release support.

  • Engineered and maintained REST API endpoints within a microservices-based platform using .NET 6/8, ASP.NET Core, and Entity Framework Core; collaborated with frontend colleagues on API request/response models and Jira requirements.
  • Consumed and integrated GraphQL and internal APIs to support business requirements.
  • Analysed and refactored SQL Server and PostgreSQL stored procedures to improve execution speed, maintainability, and backend efficiency.
  • Implemented event-driven components using AWS SNS and worked with AWS EC2 and IAM, alongside JWT authentication workflows.
  • Supported release activities by preparing release and rollback scripts, maintaining release documentation, and providing live release support using Git, Bitbucket, Jenkins, and Octopus Deploy.
  • Contributed to testing, code quality, and observability using tools including xUnit, SonarQube, and Coralogix.

Outcome and learning

Contributed to ongoing platform delivery, backend functionality, issue resolution, and system integration in a sensitive payment-processing environment.

Scope note: A payment-reconciliation initiative also involved reviewing an AI-assisted codebase and documentation (React, TypeScript, Vite, Tailwind CSS, Zustand, and Supabase/PostgreSQL), understanding workflows and hosting, and joining client discussions to prepare for future feature work. This was analysis and preparation work, not an end-to-end implementation.