Summary of the procedure

How should an accounting firm and clients currently invoicing in Excel move to e-invoice?

Short answer

Treat the change as two coordinated workflows: one for the accounting firm and one for each client, covering both issued and received invoices. Select the delivery-service arrangement, agree responsibilities and access, define how valid XML is created from the client’s source data, route issued and received documents, and test their import and review before accounting entries are posted.

1. Choice of solution

Each client decides for himself

An accounting firm can help by authorization; common provider is not a legal requirement.

2. – 3. Informing and decision of the client

Same or different provider

The Excel client chooses the postman according to his needs.

4. – 5. Data flow

Documents issued and received

XML generation, sending, downloading and forwarding to the accountant.

6. Import and control

In the accounting system

The error is not corrected by rewriting the sent XML, but by a subsequent correction document according to the nature of the change.

Detailed explanation

Step 1 — The accountancy firm assesses the capabilities of its accounting system and determines whether it will receive documents via integration, delegated access or controlled XML export. Step 2 — Each client assesses whether they fall under the mandatory regime and selects a solution; the accountant may only act within the scope of the authorisation granted. Step 3 — Using the same provider may simplify operations, but this is not required by law and does not automatically guarantee the accountant access. Step 4 — Data from Excel must be converted into a valid, structured e-invoice; an XLSX or PDF file on its own does not constitute an e-invoice. Step 5 — Verifiable sending, receipt, import and archiving of the original XML are set up. Where a delivery service is used, its statuses are also monitored; any other method of transmission is only possible with the recipient’s consent in accordance with Section 85o(2). Step 6 — Once sent, the original XML is not overwritten silently. If data needs to be amended, a follow-up document is created which clearly refers to the original invoice and contains the original number and the amended data in accordance with Section 85o(5).

As set out in the Act

The obligation to issue and send e-invoices via a certified delivery service from 1 January 2027 arises from Section 85o of Act No. 222/2004 Coll. on VAT, as amended by Act No. 385/2025 Coll., for taxable persons under Section 4, Section 4b and Section 4c. The obligation to be able to receive e-invoices stems from Section 71 of the same Act and applies to taxable persons and legal entities more broadly.

Practical examples

An accountancy firm selects a e-invoicing delivery-service provider via the Slovak Financial Administration portal for itself and for dozens of authorised clients at once.
The client switches from Excel to a simple application provided by the same service provider used by their accountancy firm, and uses this to send and receive invoices.
e-invoices received from VAT payers are routed to the client’s inbox with the e-invoice provider, from where they are forwarded to the accountant for processing.

Most common mistakes

“The whole process is a single step — simply choose a service provider and everything else is taken care of automatically.” It actually involves several separate steps (selection, informing the client, data flow for both issued and received documents, import) which need to be set up one by one.
“The client must use exactly the same post office as their accountancy firm.” The client can also choose a different provider, but in that case, the transfer of documents between them and the accountancy firm must be set up.
“The procedure is the same for both issued and received invoices.” Issued and received invoices have different data flows — one goes out from the client, the other comes in to them from suppliers.

Conclusion

The transition combines provider selection, client decisions, defined flows for issued and received documents, and controlled import into the accounting system before posting.

Legal basis

Act No. 222/2004 Coll. on VAT, Section 71 a Section 85o (as amended by Act No. 385/2025 Coll.)