Developer to Fix and Extend a SaaS Learning Platform

I am looking for a full-stack developer to maintain and extend an existing SaaS learning platform used by independent training providers. The application includes a student portal, course access, lesson progress tracking, an admin dashboard and subscription billing. This engagement focuses on improving the current codebase and shipping a set of product updates, rather than rebuilding the application. Stack: React/Next.js and TypeScript, a Node.js backend, PostgreSQL/Supabase, Stripe billing and a Python/FastAPI service for AI features, with deployment on AWS. Initial work: Fix subscription and enrollment edge cases. A successful payment should grant the correct course access, cancellations should follow the agreed access policy, and retried webhooks must not create duplicate records. Update the student dashboard and course pages. Improve responsive layouts, lesson navigation, loading states and error handling, and fix cases where lesson progress does not save. Extend the admin dashboard with course enrollment reports, student search, filters and CSV exports. Restrict each training provider to its own students and content. Add an API integration with an email platform so enrollment and course-completion events trigger the appropriate notifications. Include webhook validation, retries and logging. Extend the AI course-support assistant to answer questions using approved course materials, cite the relevant lesson and retrieve a student's progress through permission-checked tools. Improve conversation history and handling of unanswered questions. Review dependencies, fix backend API errors, add regression tests and improve deployment checks without disrupting existing users. Start by reviewing the codebase and reproducing the highest-priority issues. Then agree a short implementation plan and deliver the billing/access fixes and student-dashboard updates first. Handle reporting, integrations and AI changes as separate follow-on tasks. I need someone comfortable working in an unfamiliar production codebase, tracing issues across the frontend and backend, and making changes without introducing regressions. Please share similar SaaS maintenance, API integration or AI application work and explain how you would test the subscription-access flow. Deliverables: pull requests with documented changes, automated tests for the affected workflows, a staging demonstration, a production deployment with a rollback plan, and updated setup notes.