A practical guide for gaminco clients

This article was prepared by gaminco as a practical, clear explanation of KSeF obligations, without unnecessary legal complexity. It explains exactly what is changing, who is responsible for what (Client vs gaminco), how to prepare a company for KSeF, and how to operate safely after go-live. The text reflects current regulations, business realities, and gaminco's implementation experience.

KSeF is the central platform of the Ministry of Finance through which businesses issue sales invoices, receive purchase invoices, and obtain the KSeF number that serves as the invoice's official identifier. Once an invoice is accepted by KSeF, it is legally considered both issued and delivered, which means traditional channels (PDF and email) no longer have legal effect in VAT settlement. Keywords: KSeF, National e-Invoice System, structured invoice, VAT.

One of the most common sources of problems is an unclear split of responsibilities, so roles must be defined explicitly. The client remains responsible for organizational decisions, formal approval of accounting policy and KSeF procedures, post-implementation KSeF monitoring, response to system alerts and errors, and ensuring access to systems and data. Tax liability always remains with the client. gaminco provides paid implementation support, including preparation and updates of accounting policy, KSeF procedures (including emergency mode), instructions and checklists, support with token generation, configuration and testing in Systim.pl, sales and purchase invoice testing, and training. gaminco does not provide ongoing KSeF monitoring or regulatory monitoring after implementation.

Key dates: Stage 1 – February 1, 2026 – mandatory for the largest taxpayers whose 2024 sales exceeded PLN 200 million. Stage 2 – April 1, 2026 – the obligation extends to other businesses. Stage 3 – January 1, 2027 – micro-businesses with sales up to PLN 10,000 per month join the system. Until the end of 2026, taxpayers may still use paper invoices, cash-register documents, and fiscal receipts with the buyer's NIP for sales up to PLN 10,000 and in cases related to MPP and KSeF numbering transitions. From February 1, 2026, sending invoices with attachments will be possible after prior notification in e-US. A proper rollout should be staged: scope and obligation analysis, organizational setup and role assignment, documentation (accounting policy and procedures), access rights and powers of attorney, KSeF token setup, configuration in Systim.pl, testing, and go-live.

After implementation, the client moves into day-to-day operation, which requires regular actions: daily review of purchase invoices in KSeF, verification of sales-invoice statuses and KSeF numbers, response to system messages, and timely submission of settlement documents. Missing these actions is the most common cause of errors and penalties.

Regulations allow an emergency mode when KSeF is unavailable or access is interrupted. In that case, the client issues an invoice outside KSeF, marks it as an OFFLINE INVOICE, then enters it into KSeF after the outage and keeps event documentation. Emergency mode is an exceptional procedure and requires follow-up data completion.

KSeF is not just a technical change; it is also organizational and procedural. That is why clients can order paid implementation and training support from gaminco, delivered by specialists in line with the current price list. Support includes, among others: accounting-policy updates, KSeF procedure design, a document package (procedures and checklists), help with token generation, KSeF configuration and testing in Systim.pl, and implementation training for the client or team with individual pricing. These services are one-off implementation services and do not include ongoing post-go-live KSeF monitoring.

KSeF is a mandatory VAT invoicing system. An invoice is valid only after acceptance in KSeF. Tax responsibility always remains with the client. gaminco provides implementation support only, not ongoing monitoring. A properly executed rollout reduces risk and cost.