Poland's Krajowy System e-Faktur (KSeF) makes structured B2B e-invoicing mandatory in 2026 — phased from February for large taxpayers and April for everyone else, driven by turnover thresholds. Every B2B invoice must be issued as FA(2) structured XML, submitted to the national KSeF gateway, and is only legally "issued" once the platform returns a UPO (Urzędowe Poświadczenie Odbioru) with an official KSeF reference number. ERPNext core gives you Sales Invoice, tax templates, and print formats, but it has no concept of the FA(2) schema, no clearance session against the Ministry of Finance API, and no place to store the KSeF number or the UPO. Once the mandate is live, a PDF or a plain ERPNext invoice is not a valid invoice in Poland — and that is exactly where native ERPNext runs out of road.

ECOSIRE builds a proper Frappe app (for example erpnext_ksef_pl) that installs cleanly onto your bench and plugs into the ERPNext document lifecycle rather than bolting a script onto the side. We map your Sales Invoice, Customer, Company, and Item tax data onto the FA(2) XML structure, validate it against the official XSD before anything leaves your server, and open an authenticated KSeF session to submit the invoice for clearance. A custom KSeF Submission DocType records the request payload, the returned reference number, the processing status, and the UPO document, so every cleared invoice has a complete, queryable audit trail linked back to its Sales Invoice.

Technically, the integration is wired through hooks.py document events — on_submit of Sales Invoice enqueues a background clearance job, so submitting an invoice is never blocked by network latency to the gateway. A scheduler event polls pending submissions for their UPO and flips status the moment Poland confirms them, with automatic retry and back-off on transient gateway errors. Whitelisted server-side methods expose "submit to KSeF", "fetch UPO", and "download official XML" as buttons on the invoice, and the same methods are reachable over the Frappe REST API for headless or upstream-system use. Threshold-based rollout is handled as configuration: a KSeF Settings single DocType holds your environment (test vs production gateway), authentication token/certificate, effective mandate date, and a toggle to run in parallel/observation mode before your obligation starts — so the same build serves you both before and after your turnover threshold triggers the requirement. Role profiles and permissions restrict who can authenticate to KSeF and who can only view submissions, and client scripts surface clearance status and the KSeF number directly on the invoice form.

Because this is build-to-order, we do not hand you a generic download — we start from a short scoping call, confirm your ERPNext version (v15 or v16), your invoice volume, and your specific FA(2) field mappings, then build and validate against your real chart of accounts and tax setup. Typical delivery is one working week from confirmed scope. You receive the installable app source, a UAT pass on a staging bench with a rollback plan, technical documentation, a user guide plus a training session, and a post-go-live support window while your first real invoices clear through KSeF.