Senior Backend Developer - C#

We are seeking a Senior C# / .NET Backend Developer for an immediate-start, short-term contract position on a US HealthTech platform.

You will be stepping in to take full technical ownership of our serverless backend architecture. You’ll be maintaining and building critical features around complex Stripe billing engines, third-party vendor integrations (OAuth2, Firebase, Checkr), and AWS infrastructure.

What You Will Do:

• Daily development in C# / .NET (8/9) within a production AWS Serverless stack.
• Maintain and refine complex server-side Stripe logic (webhooks, custom invoice items, two-stage shift counting, and tier-crossing subscription models).
• Build and manage server-to-server integrations (Firebase Admin SDK, OAuth2 workflows, pending Checkr integration).
• Manage relational DB design and queries via EF Core.
• Maintain IaC templates using AWS SAM, CDK, or CloudFormation (Lambda, API Gateway, S3, Secrets Manager, CloudWatch/X-Ray).
• Maintain high standards for code review, PR discipline, and credential isolation.

• 5+ years of experience in C# / .NET development (experience with .NET 8/9 required).
• Strong expertise in AWS Serverless services (Lambda, API Gateway, Secrets Manager, IAM, CloudWatch/X-Ray).
• Deep experience implementing complex server-side Stripe billing (custom subscription logic, webhooks, invoice items).
• Proficiency with EF Core and relational database modeling.
• Experience with server-side SDKs and third-party API integrations (Firebase, OAuth2).
• Strong Git/GitHub PR discipline and security practices.
• Ability to onboard quickly and work independently with minimal hand-holding.
• Full professional English proficiency.

Preferred Skills:

• HealthTech or workforce/shift management domain experience.
• Direct experience with Checkr integration., * Do you have direct experience with server-side Stripe integrations (webhooks, subscriptions, and custom tier billing) on AWS Serverless?