Onboarding Approval Workflow Development

I need a clean, reliable approval workflow that plugs seamlessly into both our existing web application and the companion mobile app. The flow is strictly for internal staff: a team member submits new-customer details, a manager reviews the record, and a final approver signs off before the account is activated.

The core logic must:
• Capture and store each stage (Initial submission → Manager review → Final approval) with full audit history.
• Trigger real-time email or in-app notifications so no step stalls.
• Expose REST/GraphQL endpoints that our front-end teams can call from React (web) and Flutter (mobile).
• Respect role-based access controls already in our PostgreSQL DB.

Deliverables I expect:
1. Database schema updates and migration scripts.
2. Well-documented API endpoints with Postman collection.
3. Modular service layer code (preferably Node.js/TypeScript, but I’m open to suggestions).
4. Basic UI stubs that demonstrate the three stages on both platforms.
5. A short deployment guide and test cases that prove the path from submission to final approval.

I’ll provide repo access, ERDs, and current auth tokens once we kick off. If you’ve built multi-stage approval flows before, especially across web and mobile, I’d love to see a quick demo or code snippet with your proposal.