Client: Azat.team · Extenda Retail
Fuel retail POS & Dart SDK
A Flutter desktop point-of-sale and a proprietary Dart SDK for multi-site fuel retail, integrated with ATOL fiscal printers and PAX payment terminals.
Context
Fuel stations run a till that is also a legal instrument. Every sale has to produce a fiscally valid receipt, reconcile against the pumps, and settle through a payment terminal — across a network of sites, each of which opens for business whether or not the last release went smoothly.
What made it hard
This class of system is difficult for reasons that have nothing to do with the user interface. The till has to finish a sale and produce a valid receipt whether or not the site's link to head office is up. Fiscal printers and payment terminals are physical devices with their own protocols, their own firmware quirks and their own idea of what an error is — and they cannot be mocked away, because the failure modes that matter only appear on real hardware. On top of that, the fiscal rules are set per country, so the same product has to satisfy different regimes.
What I built
- A Flutter desktop point-of-sale for multi-site fuel retail operations
- A proprietary Dart SDK wrapping device access behind one interface
- Integration with ATOL fiscal printers and PAX payment terminals
- A JavaFX self-service kiosk terminal
- Serverpod backend services behind the till
Results
- >99.5% checkout uptime
- 12 tills across 4 sites, over 6 months in production (Jan–Jun 2026). Blackbox probes once a minute against /health and against a real order-placement scenario, plus Sentry for 5xx. Downtime counted as two or more consecutive failed probes. Planned deployments were not excluded from the figure.
Stack
- Flutter
- Dart
- Serverpod
- JavaFX
- ATOL
- PAX
- PostgreSQL