Nancy Fares.

Payments

The upgrade that never charged VAT

Every subscription upgrade was under-charging. Upgrade quotes were computed exclusive of VAT while renewals were inclusive — and the amount sent to the payment provider was supplied by the client rather than recomputed on the server.

The trap was the evidence: one tier looked clean, so the theory became "it only affects some plans." It didn't. That invoice had been edited before I compared it. An invoice is not independent evidence — you have to check who last modified it.

Fixed: quote made VAT-inclusive, tax applied after discounts, and the bypassed payment-verification step replaced with a real server-side amount guard. Shipped without needing a client release.

Distributed time

Bookings two hours in the past

Members at the Spanish club were losing their cancellation window early. Club-local wall-clock times were being stamped with the head-office UTC offset, so every booking was stored two hours early — three in winter.

It had been invisible for months because the display layer compensated in the opposite direction. The app looked correct. A naive wall clock is safe right up until something compares it against real elapsed time.

Fixed at the storage boundary and deployed to production.

Revenue

A discount rule nobody was reading

Coupons carried a plan-scope restriction, configurable in the admin UI, that no code path ever checked. Staff had been setting it for months believing it was enforced. It was decoration.

Gap identified, revenue exposure quantified, enforcement shipped across both the purchase and the upgrade flows.