Backend developer — medical billing data system (HIPAA, claims + ERA processing, PostgreSQL)

We're a US mental-health billing company and we're building an internal system that collects our clients' insurance claims and payment reports (ERAs) into one secure database, helps prevent claim denials, and drafts appeal letters with AI. Fixed-price, milestone-based, all payments through Upwork escrow — and an ongoing monthly retainer afterward for the right person. You'll work directly with the owner. I've run mental-health billing for years and manage many teams. I'll supply real sample files, explain any billing concept you need, and answer questions fast. You bring the engineering; I bring the billing knowledge. You will not be figuring out the healthcare side alone. WHAT YOU'LL BUILD (the foundation first): 1. A secure PostgreSQL database for claims and payment data 2. A secure upload portal or SFTP drop our teams put files into 3. A parser for standard billing files — X12 837 claims and 835 payment/ERA files — using an existing EDI library, not written from scratch 4. Auto-sorting that assigns every record to the right practice using the IDs inside each file, with an exceptions list for anything unmatched 5. Privacy protections: tokenized patient identifiers, encryption in transit and at rest, access logging (this is HIPAA data — hosting must support a BAA) 6. De-duplication and correct handling of payment reversals and secondary-insurance payments 7. A simple admin screen — data by practice, exceptions list, upload log Then, later milestones on the same contract: a claim-checking step that flags likely denials before submission, and an AI step (OpenAI/Anthropic API) that drafts appeal letters from denial data. REQUIREMENTS: - 3+ years of backend development (Python or Node) with strong PostgreSQL — required - Proven careful handling of sensitive/private data: encryption, access control, key management. HIPAA or BAA experience strongly preferred — data discipline is non-negotiable - Hands-on experience with US medical billing claims / healthcare EDI (X12 837/835) is a strong plus. Not strictly required because you'll work directly with me as your domain expert — but you must have parsed complex structured file formats before and be comfortable learning EDI fast with a library - Clear written English and some overlap with US business hours TIMELINE: I expect the full MVP in roughly 6–10 weeks part-time (first files parsing within 1–2 weeks). Give me your own per-milestone estimate. AFTER THE BUILD: a monthly retainer for the developer who builds it — monitor the system, fix issues (file formats drift), apply updates, be reachable when something breaks. Steady long-term work for a reliable person. HOW PAYMENT WORKS: each milestone is funded into Upwork escrow before work starts and released when it passes a written acceptance test you'll receive up front. Final milestone includes documentation and handoff notes. All code and credentials stay in my accounts. TO APPLY, ANSWER THESE (generic proposals will be skipped): 1. Describe a project where you parsed complex structured files — healthcare EDI (X12 837/835) is ideal, but other EDI, financial, or messy real-world formats count. What was tricky? 2. How do you protect sensitive identifiers in a database — tokenization, encryption, key management? Any HIPAA/BAA experience? 3. How do you prevent double-counting when the same file is uploaded twice? 4. A payment file can reverse or partially pay an earlier claim — how would you design the data model to handle that correctly? 5. Your timeline. 6. Are you interested in the ongoing monthly retainer after the build? State your monthly rate, what it includes, and your response time when something breaks.