C# / .NET Desktop Developer — Windows Agent

About the Project We’re building the desktop agent for a cloud-connected application. The agent is a small Windows 11 application that runs on a customer’s PC. It connects to a variety of payment gateways in the local network and forwards communications to our cloud backend via REST API. This is a self-contained build with a clear spec. You’ll own the agent end to end, working against our documented integration interfaces and cloud API. You’ll need to create new APIs if requires. What the Agent Does • Polls and communicates with local payment gateway using a variety of methods: HTTP/JSON API calls, file-based data exchange, and local URL/API interfaces — listing records and fetching individual entries and etc. • Parses data payloads in multiple formats including XML, CSV, JSON and plain text. The XML can contain binary sections, so byte-fidelity matters. • Maintains a persistent secure connection to the cloud (WebSocket Secure / WSS on port 443, outbound-initiated for NAT/firewall friendliness) plus an HTTPS REST channel for pushing data. • Queues and pushes completed records to a REST API as a JSON envelope (XML embedded as base64), handling retries, duplicates, and connectivity drops gracefully. • Shows a lightweight UI for status, connection state, and basic operator actions. Recommended architecture (open to discussion): a headless background worker / Windows Service for all connectivity and queueing, with a thin WPF UI on top. The workload is I/O-bound, not compute-heavy. Requirements Hardware & Environment • Must have your own computer running Windows 11 — the agent targets Windows 11 and you’ll need to build, run, and test on it natively. Experience & Skills • 8+ years building production C# / .NET applications (.NET 8 or later). • 3+ years building production PHP Laravel applications (version 11+) • Windows desktop development — WPF (or strong WinForms/desktop background to ramp quickly). • REST APIs — confident consuming HTTP/JSON services with HttpClient: auth headers / bearer tokens, status-code handling, retries/backoff, idempotency. • Web services in general — understands HTTP semantics, JSON, request/response contracts, and how clients behave behind NAT/firewalls. • XML, CSV, JSON and text data formats — solid working knowledge: parsing and reading structured XML (XDocument / XmlReader), navigating a schema (XSD), handling encoded/binary content cleanly; reading and writing CSV and plain-text data files. • Async I/O patterns (async/await, cancellation, ClientWebSocket). • Resilience — sensible error handling, logging, reconnect/backoff, and offline queueing. • Able to work independently — self-directed and comfortable owning a component end to end with minimal supervision. • Testing & QA — can write unit and integration tests, perform manual QA, identify and log defects, and verify fixes against acceptance criteria. • Agentic Coding — familiar of Claude Code in coding, testing, review in the workflow. • Project Management — capable of taking on lightweight PM tasks: tracking milestones, updating task status, flagging blockers proactively, and estimating remaining effort. • Security Awareness — aware of data sensitivity and handling. • Good verbal and written communication in English — clear and professional in async written communication (Slack, Jira, Confluence) and comfortable in spoken sync calls. Tools & Workflow • Comfortable working in our toolchain: Jira (issues/sprints), Confluence (docs), Postman (API testing), Sentry (error monitoring), and Bitbucket (source control / pull requests). • Clean commits, clear pull requests, and clear written communication in English. Nice to Have • WebSocket clients (ClientWebSocket) and/or a Pusher-style real-time relay client. • Windows Service / background host packaging and installer experience (MSIX, WiX, or similar). • Experience integrating with payment gateway on a local network using varied communication protocols. • Background working against a Laravel/PHP backend (you consume the API; extra PHP work is required). Working Arrangement • Project-based / fixed scope. We’ll agree milestones and deliverables up front. • Sydney business-hour overlap required for daily sync and quick turnaround on questions. A minimum of 6 hours of genuine overlap each working day is required — you don’t need to be Sydney-based. • TimeDoctor is used for time tracking and is a condition of the engagement; please only apply if you’re comfortable with activity monitoring. • Resources provided: code, device API documentation, and XML schemas (XSD). You’ll have access to a staging cloud environment to test against. Deliverables • A working, installable Windows 11 agent that communicates with payment gateway, parses data in XML/CSV/JSON/text formats, and pushes records to the cloud API per spec. • Reconnection / offline-queue handling that survives network drops and PC restarts. • Source code in our Bitbucket repo, with a brief README covering build, configuration, and install. • Basic logging suitable for diagnosing field issues. • Full deployment script and solution. How to Apply Please include: • Relevant C#/.NET desktop and REST integration work — links or descriptions of comparable projects. • Relevant PHP Laravel work — links or descriptions of comparable projects. • Your experience with XML/CSV/JSON text parsing and any WebSocket / real-time work. • Examples of working independently and owning a project component end to end. • Any Testing, QA, or light project management experience. • Your time-zone and the daily hours you can overlap with Sydney. • Confirmation you run Windows 11 and are comfortable using TimeDoctor, Jira, Confluence, Postman, Sentry, and Bitbucket. • A rough estimate / milestone breakdown for a project of this shape, and your rate. Candidates who address the multi-device integration, data-format handling, and secure-push flow directly (rather than a generic CV) will be prioritised.