KSeF and invoice attachments: how to redesign your process

Many KSeF projects skipped a detailed analysis of the internal invoice handling process and focused mainly on integrating with the government platform. Only later did it become clear that handling e‑invoices alone is not enough – you also need to link them with acceptance protocols, delivery notes, waybills and contracts. How do you design an attachment-handling process that stays compliant with KSeF and still keeps your off-system documents under control? In this article, you’ll see an approach that combines KSeF requirements with a clean, structured document workflow across the organisation.

Table of contents

1. What can be an invoice attachment in KSeF?
2. What types of attachments are not supported by KSeF?
3. How to handle attachments sent outside KSeF and integrate multiple information channels?
4. Who has access to invoice attachments in KSeF?
5. Summary

What can be an invoice attachment in KSeF?

In the Polish National e-Invoicing System (KSeF), an attachment is additional XML data embedded directly in the structured invoice. Any information entered in the Zalacznik field becomes an integral part of the structured invoice. This field appears only once on the invoice, so you cannot add multiple attachments.

The data placed there must relate exclusively to the settlement of the specific transaction (meaning it expands the information from the main body of the invoice) and may be presented as tables or other structured data blocks.

This means that a KSeF attachment can include, for example:

• a breakdown of energy/gas consumption by periods, zones, meters or tariffs;
• detailed call / bundle listings for telecom services;
• pay-per-use settlements for subscription services;
• technical parameters, serial numbers, locations, production batches;
• data required under customer contracts but too extensive for the standard invoice section (e.g. detailed service delivery reports, telemetry data packages, payment schedules).

To start adding attachments to your e-invoices, you must first submit an electronic notification to the tax administration. Only after you receive an official email confirmation from the authority can you issue and send invoices with attachments through KSeF.

You do not need this approval if you only receive e‑invoices that already contain attachments.

What types of attachments are not supported by KSeF?

Attachments in KSeF are no longer PDF files and they do not function as standalone business documents. In practice, this means the following do NOT pass through the government platform:

• contracts
• quality / compliance documentation
• correspondence
• general terms and conditions (GTC / OWU)
• manuals and instructions
• acceptance reports
• goods issue notes (WZ)
• waybills
• proof of delivery.

The lack of a permanent, automatic link between the e‑invoice and its underlying business documentation creates a significant business risk. Difficulty in quickly proving that a service was actually delivered during a tax inspection or external audit may become grounds for challenging tax-deductible costs or VAT deductions.

Because documents such as goods issue notes and acceptance reports remain outside KSeF, organisations need an efficient way to connect these fragmented information channels.

How to handle attachments sent outside KSeF and integrate multiple information channels?

A lot depends on the scale of your business. In smaller companies, a dedicated email inbox where invoice attachments are collected (along with, for example, foreign invoices and any documents that exist outside KSeF) may be sufficient.

However, organisations processing hundreds or thousands of invoices need to go a step further. The best approach is to implement an electronic invoice workflow integrated with both your document workflow and ERP system. The tool that bridges these environments is the KSeF Connector by GoNextStage. With the Connector, invoices from KSeF are automatically fed into your document workflow system.

You can close the entire process of linking a KSeF invoice with an attachment in six steps:

1. Reading structured data: right after the e‑invoice is received, all structured data is read. If the Zalacznik field is populated, the attachment is rendered and easily accessible.
2. Saving data in the invoice workflow: all information is stored in your electronic invoice workflow. This is the key moment, because the data from the invoice will later be used to match the invoice with its attachment.
3. Capturing attachments outside KSeF: the next step is to receive the attachment that exists outside KSeF, such as an acceptance report, and add it to the document workflow system. The most convenient way is to connect the dedicated email inbox mentioned above with your document workflow or broader business orchestration platform, such as WEBCON.
4. Automatic import from the mailbox: the system automatically pulls attachments from the specified mailbox, reads the data contained in the message and saves everything in the system.
5. Matching invoices with attachments: the system then links the invoice received from KSeF with the attachment delivered via email, based on, for example, the KSeF invoice number, purchase order number and similar identifiers. The user receives a notification that an attachment is available.
6. Archiving and audit trail: finally, the document is archived. Thanks to the recorded activity history for each document, you can see who did what and when, and at which point delays occur.

A process organised in this way keeps things tidy, helps you avoid duplicate work in the finance team, connects documents into a single, efficient workflow and ensures consistent information flow across the organisation. It also provides a convenient way to handle foreign invoices that fall outside KSeF.

An important benefit of integrating your systems via the KSeF Connector by GoNextStage is the ability to manage access rights to attachments or specific types of invoices.

Who has access to invoice attachments in KSeF?

If you work only in the government KSeF portal, any user who has access to your KSeF profile sees all invoice data – including attachments.

You gain real permission control only when you integrate KSeF with your own invoice workflow via the KSeF Connector by GoNextStage.

In a system like WEBCON, you can grant access to attachments (or even to specific invoice types) based, for example, on:

• invoice sender – e.g. customers assigned to the sales department, or building materials suppliers assigned to purchasing departments;
• user role in the process – e.g. requestor, budget owner, approver, accounting, controlling;
• organisational affiliation – department, business unit, company within the group, location;
• document parameters – invoice type (cost, CAPEX, sales), amount threshold, currency, counterparty country, channel (KSeF / outside KSeF);
• link to a project or contract – access limited to the project team, contract owner or a specific cost centre.

Choosing the right business logic ensures that each role sees exactly the information it needs to perform its tasks. This reduces the risk of unauthorised data access, makes IT security audits easier and clarifies accountability for decisions made at each stage of the process.

Summary

Designing a process for handling invoice attachments from KSeF requires a broader perspective than just integrating with the government portal. The National e‑Invoicing System structures the invoice itself and allows some data to be added as an XML attachment, but all other documents – acceptance reports, goods issue notes, waybills, contracts or quality documents – still live outside of it. By connecting KSeF with your electronic document workflow and systems such as WEBCON using the KSeF Connector by GoNextStage, you create an end‑to‑end process, reduce duplicated effort and gain full visibility into every action taken on each document – including foreign invoices that fall outside KSeF.