Scope
I architected and delivered the entire backend alone — from an empty repository to a live product — across 48 database migrations and 390+ merged pull requests.
The wallet ledger
Balances are derived from an append-only transaction ledger rather than stored in a column. This eliminates write-race conditions between concurrent session charges and top-ups, and keeps the full transaction history as an auditable source of truth.
Session termination
An idempotent dual-path termination flow — webhook-driven for voice calls, client-triggered for chat — with a per-minute reconciliation job as a safety net for missed provider webhooks.
Payment gateway migration
Mid-project I led a migration across both payment collection and payouts, preserving the existing transaction ledger and requiring no changes to session or balance logic. I also shipped a backward-compatible admin refund mechanism that needed no mobile client release.
Integrations
Five external services in total — telephony, payment collection, payouts, OTP and messaging, and real-time chat — plus Aadhaar-based expert identity verification.