Backend Engineer (.NET) – WhatsApp/WABA

Job Title: Backend Engineer (.NET) – WhatsApp/WABA Location: Prishtina, Kosovo COMPANY OVERVIEW Sent is building the messaging infrastructure that powers how businesses communicate with their customers. We provide a unified API for SMS, WhatsApp, iMessage, and RCS, making it simple for developers to reach people across multiple messaging channels. Following our recent Series A funding, we're growing rapidly and building the future of business messaging. POSITION SUMMARY We are looking for an experienced Backend Engineer (.NET) with hands-on WhatsApp Business Platform (WABA) experience to join our engineering team in Prishtina. In this role, you will build and maintain the core backend services that power Sent's messaging infrastructure, with a particular focus on our WhatsApp integrations. You'll work on APIs, messaging workflows, webhooks, message templates, delivery events, and backend systems that process large volumes of messages every day. You'll work closely with our engineering and product teams to build reliable, scalable messaging systems and strengthen Sent's integration with WhatsApp and other communication channels. KEY RESPONSIBILITIES - Design, build, and maintain backend services using C#, .NET, and ASP.NET http://ASP.NET Core. - Build and maintain integrations with the WhatsApp Business Platform (WABA), WhatsApp Cloud API, and related Meta APIs. - Develop and maintain WhatsApp messaging workflows, including message sending and receiving, webhooks, templates, delivery statuses, and messaging events. - Design and maintain RESTful APIs that power Sent's multi-channel messaging platform. - Integrate Sent's platform with Meta/WhatsApp, carrier networks, third-party messaging providers, and internal services. - Build reliable systems for processing asynchronous messaging events, retries, failures, and high-volume traffic. - Monitor and improve the reliability, performance, and scalability of backend services. - Identify bottlenecks, optimize database queries, and evolve database schemas as the platform scales. - Troubleshoot production issues and external API or messaging integration failures. - Participate in technical design and architecture discussions to improve the security and scalability of Sent's backend systems. - Collaborate closely with Product, Frontend, DevOps, and other Backend Engineers to deliver end-to-end features. QUALIFICATIONS & SKILLS - 3+ years of professional experience with C# / .NET / ASP.NET http://ASP.NET Core building production backend services. - Hands-on experience with the WhatsApp Business Platform (WABA), WhatsApp Cloud API, or WhatsApp Business APIs. - Experience working with WhatsApp messaging workflows, including webhooks, message templates, delivery statuses, and messaging events. - Strong experience designing, building, and maintaining RESTful APIs. - Strong understanding of asynchronous systems, webhooks, queues, retries, and event-driven architectures. - Solid knowledge of relational databases, including schema design, efficient queries, and data integrity. - Strong understanding of authentication, authorization, API security, and secure backend development. - Experience troubleshooting production integrations and third-party API failures. - Strong security and reliability mindset. - Strong written and verbal English communication skills. - Ability to work effectively with engineering, product, and other cross-functional teams. - Experience with WhatsApp Business Solution Providers (BSPs), Meta Business Manager, phone number onboarding, or WABA configuration is considered a strong advantage. - Experience with CPaaS, telecommunications, SMS, RCS, messaging infrastructure, or high-volume communication platforms is considered a strong advantage. - Experience building high-availability or high-throughput systems is considered a strong advantage. WHAT WE OFFER - Work with an experienced engineering team on products used by customers worldwide. - Work on high-scale messaging infrastructure across WhatsApp, SMS, RCS, and other communication channels. - Meaningful ownership of the systems and integrations you build. - Competitive salary based on experience. - Career growth opportunities in a fast-growing US technology company. - Private health insurance (including 50% family coverage). - Monthly gym membership allowance. - Modern office in central Prishtina. - Snacks, coffee, and refreshments in the office. - Regular company and team activities. - In accordance with Kosovo Labor Law. OFFICE LOCATION - Prishtina, Kosovo. WORK SCHEDULE Monday–Friday, standard business hours, 9:00 AM–5:00 PM. Fridays are remote.