# Keto Kartel — Subscription Commerce Without the Double Charges and Data Chaos

> Subscription businesses are complex: customers upgrade, pause, skip weeks, swap products, and cancel mid-cycle. Keto Kartel's original system couldn't handle these state changes cleanly — double charges and inventory errors were a regular occurrence. We rebuilt the subscription engine with an idempotent billing core and it's been zero incidents since.

## Project context

- Client: Keto Kartel
- Industry: Health Food & Subscription
- Year: 2023

## Challenge

Double charges from billing retry races. Incorrect prorations when customers changed plans mid-cycle. Inventory phantom reservations from failed-then-retried billing attempts. Customer service was handling dozens of billing complaints monthly — a direct cost in refunds and staff time that was eating into margins.

## Solution

Schema redesign with explicit state transitions and timestamps. Idempotency keys on every billing operation — the same key submitted twice produces one charge, always. Inventory deduction as a confirmed-billing-event subscriber, never at order creation. Proration logic based on time-weighted state history, not current state at billing time. Zero double charges since deployment.

## Services

- Web Development

## Published results

- 0 Double-charge incidents (post-launch)
- −100% Billing complaints (monthly) (vs pre-rewrite)
- 6 Subscription tiers handled (cleanly, no edge case)
- eliminated Inventory phantom reservations (event-driven deduction)

## Benefits

- Idempotent billing — physically impossible to double-charge
- State-transition schema — accurate proration always
- Inventory only decrements on confirmed billing event
- 6 subscription tiers with full plan-change flexibility

## Source and contact

- Canonical project page: https://qualityx.co/en/portfolio/keto-kartel-subscription
- Discuss a related project on WhatsApp: https://wa.me/905392376734