Our API integration services connect your shop, ERP, CRM, payments, Allegro (Poland's largest online marketplace) and KSeF, Poland's National e-Invoicing System, so that orders, invoices and statuses move between systems without being retyped. If a system has API documentation, we can integrate with it.
What is API integration? It is a connection in which programmes exchange data on their own. Among other things, we connect:
Sending invoices in the FA(3) structure from your system and downloading purchase invoices without logging in to KSeF, Poland's National e-Invoicing System, by hand.
Orders and statuses from your online shop inside your own system, and invoices attached automatically to orders on Allegro.
With our ERP integration services, documents, business partners and stock levels stay synchronised between your ERP, accounting software and shop.
Enquiries from forms go straight into your CRM together with their source, and your salesperson can see the customer's orders and invoices.
Payment gateways and recurring payments that change the order status and send a confirmation on their own.
If your system has no API, we design one so that other tools can connect to it securely.
Integration is usually the first step towards process automation: once data flows on its own, the next steps are easy to automate.
Poland's National e-Invoicing System (KSeF) is mandatory from 1 February 2026 for companies with sales above PLN 200 million in 2024, and from that date all companies receive invoices through it. From 1 April 2026 the remaining Polish VAT payers issue invoices in KSeF, and from 1 January 2027 the smallest companies with sales of up to PLN 10,000 per month do so as well.
There are no penalties until the end of 2026. From 1 January 2027, failing to issue an invoice in KSeF carries a penalty of up to 100% of the VAT amount on the invoice, and up to 18.7% of the gross amount for invoices without VAT. On 20 October 2026 the Polish government adopted a draft act that would postpone these penalties until the end of 2027. The draft is already in the Sejm (print no. 3245): the first reading took place on 21 October 2026 and the draft was referred to the Public Finance Committee. Until the act enters into force, the current rules apply. The KSeF obligation itself from 1 January 2027 does not change.
We cover the details in our articles on penalties under KSeF from 2027, integrating KSeF with your own system, shop or ERP and importing purchase invoices from KSeF.
We calculate it the same way as any integration: hours × €46 net (excl. VAT). Indicative price ranges:
Euro amounts converted at the NBP mid-market rate of 14 September 2026 (€1 = 4.3391 zł) and rounded. We invoice in PLN.
Our article on importing purchase invoices from KSeF breaks down the hours for receiving invoices block by block.
The ranges above do not include 12–24 hours for architecture, logging and deployment of the whole project — the cost calculator adds them to its result. In the calculator choose KSeF (the connection, 24–60 hours with a documented API), and for receiving purchase invoices tick “KSeF: receiving purchase invoices” or “KSeF: full purchase invoice workflow” among the extras — it will then show the range for that scope.
The timeline depends on whether your system has an API: with a documented API we are talking weeks, while a system without an API adds time for investigation. We give you specific price ranges within 2–3 working days of reviewing your systems — free estimate or project brief.
We do not advise on tax matters. Confirm the scope of your company's obligations with your accountants, and we will take care of the technical side.
We work on an hourly basis: programming €46/h net (excl. VAT). The API integration cost depends on the number of systems being connected, the quality of their API documentation and the number of exceptions to handle.
An API is a documented way for programmes to exchange data. With API integration, your systems send and retrieve information such as orders or invoices on their own, instead of you retyping it by hand.
There are ways to do it: importing and exporting files, connecting to the database, or a new API built on top of the system. First we check which route will be stable in your case.
From 1 February 2026 for companies with sales above PLN 200 million in 2024, from 1 April 2026 for the remaining Polish VAT payers, and from 1 January 2027 for the smallest companies with sales of up to PLN 10,000 per month. Penalties apply from 1 January 2027. On 20 October 2026 the Polish government adopted a draft act that would postpone these penalties until the end of 2027. The draft is already in the Sejm (print no. 3245): the first reading took place on 21 October 2026 and the draft was referred to the Public Finance Committee. Until the act enters into force, the current rules apply. The KSeF obligation itself from 1 January 2027 does not change.
The cost is the number of hours times €46 net (excl. VAT). The number of hours depends on where the invoices are created, how many there are and whether the system has an API. We give you a price range within 2–3 working days of reviewing the system.
Yes, and from 1 February 2026 it is mandatory for every company, regardless of sales volume. Receiving means downloading the invoice, saving the KSeF number, matching it with the counterparty and the order, linking credit notes to the original invoice, and handling errors and retries.
Sending invoices takes 24–60 hours of work, receiving purchase invoices 38–100 hours, and the full receiving package with an approval workflow, attachments and an archive 78–202 hours. With a system that has a documented API we are talking weeks; a system without an API needs extra time for investigation.
Yes. The Allegro API allows up to 10 PDF invoices per order, each up to 3 MB, so the invoice from your system reaches the buyer without any manual uploading.
Describe them in the project brief. We will reply within one working day, and prepare a free price range and schedule within 2–3 working days.
Fill in the brief