Telco payment gateway integration

Recurring subscription billing at national scale, against a telco billing API with strict rate limits, partial failures and no idempotency guarantees. Every failed charge is a customer who thinks they paid.

An idempotent charge pipeline with per-subscriber scheduling, exponential backoff, and a reconciliation job that compares our ledger against the operator’s settlement file daily.

Celery beat schedules charge batches; workers hold a Redis-based rate limiter shared across the fleet; every attempt is written before it is made, so a crash mid-charge is recoverable. Reconciliation runs nightly and raises a human-review queue rather than auto-correcting money.