- 6+ years in test automation / SDET roles, with a focus on backend and server-side systems (not mainly UI testing).

- Strong C# / .NET coding. You build and maintain test frameworks, not just scripts (MSTest, NUnit or xUnit).

- Strong SQL Server skills : you write complex queries to set up and verify data, and you understand stored procedures, transactions and isolation well enough to test them properly.

- Experience testing APIs, services and message-based systems (queues, Kafka or similar), including asynchronous and failure scenarios.

- Comfortable on Windows Server : services, event logs, log files, configuration and troubleshooting.

- Solid test design : equivalence partitioning, boundary values, state transitions, and negative and failure-path testing.

- Experience running tests in CI/CD pipelines (Azure DevOps/TFS, Jenkins or similar) and with Git.

- Strong debugging and analytical skills, and clear written communication in defect reports and test documentation.

- Working knowledge of acquiring.

You know what to test and what "correct" looks like on the acquirer side :

- The four-party model (merchant, acquirer, card scheme, issuer)

- The transaction lifecycle : authorization, capture, clearing, settlement and merchant payout

- Refunds, reversals, offline transactions and chargebacks

- Interchange, scheme fees and merchant pricing (blended vs. interchange++)

- Reconciliation of transactions against clearing files and payouts

Need to know :

- Payment protocols and scheme formats : ISO 8583, GICC, ZVT, EMV, girocard, Visa / Mastercard clearing formats (for example Base II, IPM).

- Testing experience on an acquiring or merchant-processing platform, including scheme certification or acquirer migrations.

- Experience with payment simulators and test tools (terminal, host or HSM simulators, test card sets).

- Ability to read C++ code to understand behavior and find edge cases.

- Java / Spring Boot and REST API testing (for example REST Assured or Postman/Newman).

- Performance testing tools such as JMeter, k6, NBomber or Gatling.

- Banking file formats such as SEPA, camt or Mastercard IPM.

- Test management in Jira / Xray, and experience producing audit evidence in regulated environments (PCI DSS, BaFin, DORA).

- Experience with AWS or with testing infrastructure migrations.

- German language skills are a plus, since parts of the code, test cases and documentation are in German.