Backend/API Developer — for SaaS Onboarding & Assessment Platform

We're building the API/middleware layer for a new workforce product, Scope covers: onboarding form endpoints (a master company profile plus three product-specific supplements), the full B2C assessment submission and payment flow, a team self-serve commercial path, an in-app notification system, certificate/evidence handling for completion tracking, and an internal admin extension for our own staff — all connecting to a Supabase backend. This is structured as six clearly-scoped milestones, with full technical specification, schema references, and acceptance checklists provided in the attached brief. Payment gateway is Stripe. Three frontend reference files (the actual onboarding forms and app screens) will be provided alongside the brief so you're building against real code, not just field-name summaries. Budget: Fixed price, $800 total across 6 milestones