API Technical Lead — Payments Platform Modernization
Role type: Hands-on technical leadership
Domain: Payments / Financial Services
Primary stack: .NET Core / ASP.NET Core / C#
Experience: 12–15 years hands-on, with a minimum of 8 years as an API Lead
About the Role
We are hiring an API Technical Lead to own API architecture, design and implementation for a large-scale payments platform modernization program.
This is a hands-on role. The successful candidate will lead the API workstream while continuing to write, review and debug code. They will work within the client's established Architecture Decision Record framework, govern design quality across the API estate, and take accountability for the end-to-end integrity of the API layer — including the observability and security contracts that downstream systems depend on.
The role demands breadth of understanding across the full stack — from front end through gateway and proxy layers to backend services and cloud infrastructure — combined with the depth to identify a design defect and challenge it.
The platform is built on .NET Core and ASP.NET Core across both monolithic and microservices architectures. AI-assisted engineering is central to the modernization approach: the successful candidate will use GitHub Copilot and Claude Opus for forward engineering — code generation and modernization — and reverse engineering — code understanding, documentation and refactoring — and will take accountability for validating what those tools produce.
Key Responsibilities
Lead API architecture, design and implementation for the payments modernization program.
Own the end-to-end API call path — from UI through the interface layer, API gateway and proxy tiers to backend services and downstream systems.
Define and enforce API contracts, versioning strategy, error handling standards and integration patterns.
Design for idempotency, resilience and failure recovery across a high-volume transaction platform.
Work within and uphold the client's two-tier ADR framework: foundational ADRs covering design patterns, API standards, development guidelines, best practices and architecture alignment; and domain-driven ADRs covering the payment processing engine, payment management and account management.
Review architecture and design artifacts critically, and raise gaps, inconsistencies or omissions rather than implementing to a flawed specification.
Maintain alignment between platform-level standards and domain-level design decisions.
Hands-on development across .NET Core, C# and ASP.NET Core, spanning both monolithic and microservices-based applications.
Design, build and deploy AI-enabled architectures integrated with .NET Core and ASP.NET Core applications.
Ensure smooth integration of AI components with .NET-based enterprise systems.
Provide technical guidance on REST APIs, microservices and enterprise integration patterns.
Delivery Accountability
Guarantee the retrieval and posting contracts across the platform — ensuring downstream teams and consuming systems can access the data they need, in the right shape, with defined freshness guarantees.
Conduct code and design reviews; set and hold the technical bar for the team.
Mentor and guide .NET development teams and AI engineers, and provide technical direction across the API workstream.
Interpret ADR, HLD and LLD documentation and convert it into features and stories for the delivery team.
Support project delivery from architecture definition through to production deployment.
Drive CI/CD, containerization and automation practices across the API estate on Azure.
Embed observability into API design as a first-class requirement.
Enforce security standards appropriate to a public-facing payments API.
Use GitHub Copilot and Claude Opus hands-on for AI-assisted development across the .NET estate.
Apply AI tooling to forward engineering — code generation and application modernization.
Apply AI tooling to reverse engineering — code understandi…n, documentation generation and refactoring of existing applications.
Integrate AI capabilities into enterprise systems through secure APIs.
AI-Assisted Delivery
Operate the client's existing agentic AI pipelines — configure, execute and troubleshoot pipeline runs.
Review and validate AI-generated output for correctness, security and domain accuracy before it progresses.
Ensure designs meet enterprise standards, security requirements and scalability needs.
Support solution walkthroughs with stakeholders, delivery teams and governance bodies.
Maintain and present daily, weekly and monthly status reporting.
Collaborate with Business Analysts, Program Managers, DevOps and Security teams.
Ensure adherence to Responsible AI, security and compliance guidelines.
Must-Have Requirements
.NET & Core Engineering
12–15 years of hands-on engineering experience, including a minimum of 8 years as an API Lead.
Strong hands‑on expertise in .NET Core, ASP.NET Core and C#.
Delivery experience across both monolithic and microservices-based .NET applications.
Proficiency with Git version control.
Experience working in global delivery or offshore engagement models.
Technical Leadership
Proven experience leading API engineering teams while remaining hands‑on with code.
Ability to write, review and debug production code — demonstrable in a live technical assessment.
Strong command of design patterns, API standards, development guidelines and engineering best practices, sufficient to author or critique architecture decision records.
Strong ability to interpret ADR, HLD and LLD documentation and translate it into features and stories.
Confidence to challenge architectural decisions and eclipse design gaps constructively.
API Development & Modernization
Recent, current delivery experience on API development and modernization or re-platforming programs.
Contract-first development with OpenAPI/Swagger.
End‑to‑end understanding of API infrastructure — API gateways, facade and BFF layers, proxy chains, routing, rate limiting, throttling and caching.
Integration patterns: synchronous and asynchronous messaging, event‑driven architecture, retries, circuit breakers, timeout budgeting.
Microservices architecture and decomposition of monolithic platforms.
Payments Domain
Hands‑on delivery experience on a payments platform.
Working knowledge of payment processing engine, payment management and account management domains.
Understanding of the payment lifecycle — authorization, capture, clearing, settlement, posting, reconciliation, reversals and exception handling.
Familiarity with payment messaging standards and rails relevant to the platform.
Awareness of the regulatory and compliance environment around payments, including PCI‑DSS and audit traceability obligations.
Cloud, DevOps & Automation
Azure — hands‑on experience with API Management, AKS/App Services, Functions, Key Vault, messaging services and managed identity.
CI/CD — end‑to‑end pipeline design and ownership, including automated testing, security scanning and progressive deployment strategies.
Docker — containerization, image hygiene, multi‑stage builds.
Kubernetes — deployments, scaling, configuration and secrets management, resource governance, and live troubleshooting of running workloads.
Automation — infrastructure as code, environment provisioning, deployment and test automation.
Azure is the primary platform. Equivalent hands‑on experience on AWS is acceptable where Azure exposure can be demonstrated.
Observability
Observability is a mandatory design requirement, not an operational afterthought, because observability data must be propagated to downstream systems.
Distributed tracing designed into the API from the outset, propagated across every hop including asynchronous and queue boundaries.
Correlation ID, request ID and unique transaction identifiers carried consistently across the call path and forwarded downstream.
Structured logging, metrics and health instrumentation as design‑time concerns.
Sensitive data masking at the point of logging.
Tool‑specific expertise is not required. What matters is whether traceability and correlation are designed in.
API Security
The platform exposes a public‑facing API. Standard controls are expected as a baseline of design correctness.
OAuth 2.0 and OpenID Connect with appropriate flow selection; JWT validation, scope design and token lifecycle management.
mTLS for partner and scheme connectivity.
Object‑level and function‑level authorization.
Input validation, schema enforcement and injection prevention.
Rate limiting, throttling and abuse protection at the edge.
Encryption in transit and at rest; secrets and key management.
Sensitive data handling — masking, tokenization and minimization of PII and cardholder data.
Familiarity with the OWASP API Security Top 10.
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