The invoice is the founding document of any business, and the same errors keep appearing on the invoices of sole traders in Czechia — errors that lead to questions from the tax office, late payments or fines. This article goes through the twelve most common ones and shows, for each, how to fix it and how to stop it happening again.
If you would rather walk through issuing an invoice from the start, with the mandatory details and a worked example, read how to issue an invoice as a sole trader first.
1. Mandatory details missing from the invoice
The VAT Act (Act No. 235/2004 Coll., § 29 in particular) sets out what a tax document has to contain. For a VAT payer: the designation of the document, its registration number, the issue date, the date of taxable supply (DUZP), identification of the supplier and the customer (name, registered address, IČO, DIČ), the subject of the supply, the tax base, the VAT rate and the VAT amount.
Consequence: an invoice without the mandatory details is not a valid tax document. The customer cannot claim the VAT deduction and you risk a fine in a tax inspection.
How Taxorio prevents it: the invoice form enforces the required fields. You cannot issue an invoice without your IČO, a description of the supply or a valid date, and your own company details are filled in from Settings, so the supplier side is always complete.
2. Wrong IČO or DIČ for the customer
Typos in identification numbers are among the most frequent errors. Swap two digits and the invoice points at a non-existent — or entirely different — entity. This is particularly awkward in the VAT control statement, where the data is matched automatically.
Consequence: a mismatch in the control statement between supplier and customer. The tax office can ask both sides to explain, and in the worst case the customer's VAT deduction is refused.
How Taxorio prevents it: ARES autofill lets you enter the client's IČO alone and pulls the verified data from the ARES register — registered name, address and DIČ. No copying by hand, no typos. Eight digits and the rest fills itself in.
3. The wrong VAT rate
Since 2024 Czechia has two VAT rates: the standard 21 % and the reduced 12 % (until the end of 2023 there were two reduced rates, 15 % and 10 %, replaced by a single 12 % rate). Mixing up 12 % and 21 % is a common error, especially for goods and services sitting near the boundary between them.
Consequence: invoicing at the higher rate makes your service needlessly expensive for the end customer. Invoicing at the lower rate means you remit less VAT than you owe — and an assessment after an inspection comes with a penalty on top.
How Taxorio prevents it: you pick the rate from the values in force (21 %, 12 %, 0 %). For work you invoice repeatedly, save an item template with the correct rate once and reuse it without the risk of a mix-up.
4. Missing date of taxable supply (DUZP)
DUZP is the date the service was delivered or the goods handed over. Many sole traders leave it off the invoice or confuse it with the issue date — yet DUZP decides which tax period the invoice belongs to.
Consequence: without DUZP it is unclear which VAT period the invoice falls into, so it can end up in the wrong VAT return and control statement. The tax office can reject a tax document that lacks it.
How Taxorio prevents it: DUZP is a required field on every invoice. Taxorio prefills it with the issue date and you can change it. For the control statement and the VAT return, invoices are sorted by DUZP rather than by issue date, so the export lands in the right period.
5. Duplicate invoice numbers
Every invoice needs a unique registration number within the calendar year, forming an unbroken series. Duplicates are a classic symptom of invoicing by hand in a spreadsheet, once you lose track of the last number used.
Consequence: duplicates undermine the credibility of your records. In a tax inspection they raise the suspicion that documents have been manipulated, and they make matching payments by variable symbol harder.
How Taxorio prevents it: invoices are numbered automatically in a fixed YYYYXXXX format — 20260001, 20260002 and so on. The system keeps the sequence and never gives two invoices the same number; at the turn of the year the counter resets on its own. If you type in a custom number, though, Taxorio does not check it for uniqueness when saving (an invoice imported from a PDF only gets a warning when the same number already exists for that client), so that exception is yours to watch. Other document types carry their own prefix, so advance invoices, tax documents for a received payment and credit notes never collide with the standard series.
6. No QR payment code on the invoice
The QR payment code (the Czech SPD standard, Short Payment Descriptor) is not required by law, but without it the customer has to retype the account number, variable symbol and amount by hand.
Consequence: slower payment and a higher chance of an error — wrong variable symbol, wrong amount — which you then have to chase.
How Taxorio prevents it: QR payments are on by default; once a bank account is filled in, Taxorio places a QR code on issued and overdue invoices with a positive amount, provided you have a bank account in the currency of the invoice. The code carries the account number (IBAN), the variable symbol, the amount and the currency, so the customer scans it in mobile banking and the payment is prefilled.
7. The wrong variable symbol
The variable symbol is what matches a payment to an invoice. The usual error is a different symbol on the invoice than in the QR code, or a symbol that does not correspond to the invoice number at all.
Consequence: the money arrives but cannot be matched automatically. You end up going through bank statements by hand to work out which invoice each payment belongs to — hours of work once the volume grows.
How Taxorio prevents it: the variable symbol is derived from the invoice number and used consistently, both in print on the invoice and inside the QR code. There is nothing for the two to disagree about.
8. Forgetting reverse charge on EU invoices
When you provide a service to a VAT payer in another EU member state, the reverse charge regime applies: you issue the invoice without VAT and the obligation to declare the tax moves to the customer. Many sole traders miss this and invoice with Czech VAT instead.
Consequence: if you charge Czech VAT to an EU-registered customer, you remit VAT nobody owed and your customer cannot claim a deduction at home. Putting it right means a corrective tax document and an additional return.
How Taxorio prevents it: Taxorio offers a VIES check (VAT Information Exchange System) to confirm the foreign customer is a registered VAT payer in the EU, so you know before issuing whether reverse charge applies. You then issue the invoice at the 0 % rate and Taxorio prints the mandatory clause — "Tax to be paid by the customer", with the reference to Article 196 of Directive 2006/112/EC and § 9(1) of the Czech VAT Act — on the PDF and the web version of the invoice, in the language of the document.
9. Invoicing a foreign partner without a VIES check
Even when you intend to apply reverse charge, you still have to confirm the foreign customer really is a valid VAT payer in the EU. Without that confirmation you have no evidence the regime applied.
Consequence: if the customer turns out not to be a valid EU VAT payer, the Czech VAT is yours to remit. Reconstructing and correcting it later is slow and expensive, and you risk a penalty on top.
How Taxorio prevents it: the VIES check verifies a foreign partner's VAT ID directly against the European VIES database in one click, and records the result with the date on the client. Before you issue into the EU you can see where the customer stands.
10. Issuing the invoice late
The VAT Act requires a tax document to be issued within 15 days of the date of taxable supply. Plenty of sole traders slip well past that, especially at the end of a month or quarter.
Consequence: issuing late breaches § 28(4) of the VAT Act and the tax office can impose a fine. It also creates a problem for the customer, who needs the document for their own records.
How Taxorio prevents it: the tax calendar flags approaching deadlines with colour-coded badges. And because issuing an invoice takes a minute — from the web app, or through the MCP connector if you drive Taxorio from Claude — there is little reason to put it off.
11. No backup of your documents
Paper invoices fade, disappear in a move or get ruined by damp. Manual spreadsheet backups go with the failed disk. Meanwhile the law requires tax documents to be kept for at least ten years.
Consequence: in a tax inspection you cannot produce the documents, which leads to tax being assessed by estimate — usually not in the taxpayer's favour. Losing documents also means losing the right to the VAT deduction they carried.
How Taxorio prevents it: every invoice created in Taxorio is stored in cloud storage and available whenever you need it, with a PDF download for each one. On the expense side the document inbox reads scanned receipts and invoices and keeps the original attached to the record, and the phone scanning session means you digitise a receipt the moment you get it.
12. An invoice number format the EPO filing system rejects
The Financial Administration's electronic filing system (EPO) has specific requirements for the data in an XML filing. The VAT control statement (DPHKH1) and the VAT return (DPHDP3) need registration numbers in a consistent format, and the wrong format can get the filing rejected.
Consequence: the XML filing bounces. You correct the file and submit again, which can push you past the deadline and into a fine — and for the control statement the fine is severe: CZK 1,000 for filing late on your own initiative, CZK 10,000 to CZK 50,000 if you only file after being prompted, or not at all.
How Taxorio prevents it: automatic numbering uses the fixed EPO-compatible YYYYXXXX format. The VAT exports Taxorio generates (DPHKH1, DPHDP3) take the invoice numbers as they are and the XML is validated against the current XSD schemas of the Financial Administration before you file it.
Summary: prevention is cheaper than correction
Every one of these errors is easy to make and tedious to undo. A corrective tax document, an additional return, correspondence with the tax office — all of it costs time you would rather bill. Systematic prevention is cheaper:
- ARES autofill removes typos from IČO and DIČ
- Automatic numbering keeps an unbroken series with no duplicates
- SPD QR codes take the retyping out of payment
- VIES checks confirm a foreign DIČ before the invoice goes out
- Required fields in the form force every legal detail to be filled in
- The tax calendar flags deadlines while there is still time
- Cloud storage keeps the documents safe for the archiving period
You can try Taxorio at app.taxorio.cz. The FREE plan covers 2 invoices a month; the PRO plan from CZK 69 a month removes the limit and adds the XML exports for VAT filings.
Taxorio scope: Taxorio provides invoicing and income/expense records for Czech sole traders. It is not full accounting or personalised tax advice. For an unsupported or unusual case, verify the treatment with a Czech accountant or tax adviser before filing.