Blog
Long-form, code-heavy writing on software engineering, AI/LLM, payments and system design.
The in_app_purchase integration done properly: the purchase stream from app start, pending states, completing purchases before Play auto-refunds, and the backend validation that makes revenue real.
BLE-first control paths with replay-proof signed commands, access modeled as revocable grants, the marketplace layer for renting spots, and the fleet operations nobody demos.
What each OCPP version actually buys you, the WebSocket message choreography with real frames, a minimal CSMS endpoint in C#, and the state-management work that is the real product.
The export a German tax auditor actually asks for: master data setup, asynchronous cash point closing ingestion with its validation gotchas, and one-click TAR exports from your admin panel.
Germany now requires declaring every electronic cash register to the tax office. How to automate the whole pipeline — taxpayer, establishments, clients, XML validation and ERiC transmission — with the SUBMIT DE API.
A backend developer's walkthrough of Germany's cloud TSE: TSS lifecycle automation, client registration per BSI TR-03153, transaction signing with offline queueing, and audit-ready TAR exports.
One client per terminal, an explicit state machine, first-class timeouts and cancellation, idempotent references, verbatim receipts and the observability that keeps payment lanes boring.
Four families of payment errors, one correct reaction each: classification code, the recovery query that prevents double charges, dispute-winning logs and a test plan for the ugly paths.
Deploy payment middleware like any other workload: a production-shaped compose file, terminal networking options, log persistence for compliance and settlement-safe rollout pipelines.
The EftPeer operation lifecycle from a POS developer's seat: connect and login, purchase outcomes, reversal vs refund, recovery queries and the end-of-day settlement everyone forgets.
