Fintech installment-collection platform

Client work, anonymized until the client approves naming it.

Label: CLIENT WORK
Result: ~5,000 users live after a parallel run beside Excel
Stack: FastAPI · React Native (TypeScript) · PostgreSQL · Railway

Problem

Collections ran on Excel. The client needed ledger-grade accuracy before moving about 5,000 users onto a new system.

Approach

An immutable double-entry ledger, with reversals made by admins as new entries rather than edits.
Duplicate-UTR protection so the same bank transfer can never be recorded twice.
Cash-handover reconciliation between agents and the office.
Multi-tenancy enforced with PostgreSQL row-level security.
A referral and commission engine.
An admin web portal and a multi-role Android app for clients, agents, sub-agents and admins.

Architecture

- Android app Client · Agent · Sub-agent · Admin
- Admin web portal Reversals · reconciliation
- FastAPI Duplicate-UTR guard · auth · roles
- Double-entry ledger PostgreSQL · immutable · row-level security
- Commission engine Referrals · payouts

Every money movement passes through one API into an append-only ledger. The ledger is the one part that must never be wrong, so it is drawn in red.

Result

Live with about 5,000 users, after a legacy data import and a parallel run beside the old Excel process.