Senior .NET Backend Engineer

SalesBlue is a voice AI sales automation platform for insurance brokerages in Mexico and Spain. We build outbound calling systems, campaign orchestrators, and agentic workflows integrating telephony, LLMs, carrier portals, and CRMs. Complex backend, real clients, fast pace environment. We need a senior .NET/C# engineer who has operated real production systems under load — not just built them. Someone who thinks in architecture first, can design for resilience and scale, and knows what it means to keep a highly integrated backend alive across many moving parts. Responsibilities Core backend services: campaign orchestrators, FSM-based workflow engines, API integrations with telephony (Twilio), voice AI platforms, insurance carriers, and CRMs. System design and architecture decisions alongside the CTO. Multi-server deployments, async processing pipelines, event-driven flows. Frontend integration via Next.js (familiarity needed, not the focus). Deep .NET / C# expertise. Strong CS fundamentals: OOP, SOLID, SOA, design patterns. Experience designing and operating event-driven backend architectures. Experience running systems on multi-server infrastructure with real traffic — you know what horizontal scaling, fail over, and stateless design actually mean in practice. Proficiency with parallel and concurrent programming — async/await, thread safety, queues, etc.. Experience integrating many external services/APIs in a single backend — you've dealt with the chaos and know how to tame it. Ability to design backend architecture from scratch for complex web applications. Fluent in AI dev tools: Claude Code, Cursor, GitHub Copilot — part of your daily workflow, not occasional use. Communicates clearly in English; Spanish is a plus. Nice to have Voice AI / telephony integrations (Twilio, Retell, ElevenLabs, Deepgram). AWS, Vercel, or Railway deployments. Startup experience — comfortable with shifting requirements. Compensation in USD. Fully remote work High-growth opportunities in an international company.