CASE STUDY / 03 · Payment systems
Back-office migration, financial-system integrations and support-driven product changes — built on earlier experience with terminal software and PC–POS protocols.
01 / Context
After moving internally from SEP’s POS team to the payment-switch team in March 2021, I worked on back-office systems supporting banking payment operations. Requirements came directly from merchant and customer support teams, so the work connected payment-domain understanding with service behaviour and user-facing changes.
02 / Engineering decisions
Worked on migration to .NET Core and implemented C#/ASP.NET Core backend functionality with SQL Server, Dapper and Entity Framework / EF Core. This combined application modernisation with the data-access and integration work needed by the back office.
Translated support requests into backend functionality and JavaScript, HTML and CSS interface changes. This included working with REST/SOAP integrations rather than treating each UI change as an isolated screen edit.
Worked with Onion and MVC architectures, asynchronous programming and dependency injection to structure payment-system development. My domain-design experience also includes familiarity with DDD concepts.
Earlier in the POS team, developed C/C++ terminal software and C#/.NET Framework PC-POS applications, and designed a bit/packet-level communication protocol for serial and network-cable connections.
03 / System responsibilities
High-level model of responsibilities. Internal implementation details are omitted.
The production throughput figure describes team scale. The migration, integrations and product changes describe my responsibility. Keeping both visible makes the experience more useful to a technical reviewer.
04 / Validation & outcomes
The payment-switch team increased production throughput from 1,000 to 5,000 transactions per second.
Back-office .NET Core migration, backend/data-access work, integration and support-driven UI changes.
The 5× result belongs to the switch team. No standalone benchmark isolates the effect of my back-office migration.
No customer information, transaction records, payment credentials, internal diagrams or protocol specifications are included.
Diagrams and interactive examples are explanatory models. Employer code, account data and strategy logic remain confidential.
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