Hungarian Online Invoice System changes in September: New errors, new penalty risks | News Flash

Instead of the previously announced July 1 date, the NAV Online Invoice System’s controls will become significantly stricter starting from September 15, 2025. The changes affect all businesses subject to electronic invoice data reporting obligations. Out of the previously classified “WARNING” messages, 21 will now be reclassified as “ERRORS”, meaning that the affected invoice data submissions will be considered invalid and will be blocked.

What errors should businesses watch out for? Two-step invoice modification

According to NAV’s auditing experience, a common issue is the incorrect implementation of two-step invoice modifications. Many companies submit the first modification of the original invoice using the STORNO operation code. However, this is incorrect, as it prematurely closes the invoice chain.

The correct method: invoice modifications should be submitted using the MODIFY operation code, including the serial number of the modified original invoice. This change requires increased attention from any company that issues modifying or correcting invoices.

New errors and WARN messages in the Online Invoice System

As of September 2025:

• An INFO message, which was previously inactive, will now appear as a warning (WARN) if the performance date and the issue date are identical on a modifying or canceling invoice.
• A new WARN message will appear in case of incorrect VAT status reporting. This is especially relevant when customerVatStatus = OTHER, but the invoice contains a valid Hungarian tax number—e.g., in the fields communityVatNumber, thirdStateTaxId, or customerTaxNumber.

Who will be affected by the stricter error handling in NAV’s Online Invoice System in 2025?

These new error-handling rules will particularly impact businesses that:

• Trade with EU or third-country partners,
• Issue invoices in foreign currency,
• Use collective (summary) invoices,
• Regularly issue modifying/corrective invoices,
• Work with customers having group VAT numbers,
• Provide tax-exempt services.

What steps can you take to avoid penalties?

Since the 21 types of erroneous data submissions will no longer be accepted from September 15, 2025, businesses are advised to:

• Review their own Online Invoice data submission practices,
• Revisit previously received WARNING messages, and

Correct any affected errors – especially concerning two-step invoice modifications and VAT status issues.

Businesses have been granted additional preparation time and testing opportunities

To improve the quality of invoice data, the NAV will enforce stricter rules against certain types of errors starting September 15, instead of the previously announced July 1 deadline.

The NAV published the planned validation tightening as early as March 26, 2025, and sought feedback from taxpayers and software developers on the modification of 21 validation rules. Based on the responses received, it became clear that the changes would require not only technical updates but also operational adjustments in invoicing software. As a result, the NAV is providing a testing period between September 1 and 15 in the Online Invoice test environment.

What can businesses do?

• It is advisable to review invoicing processes, especially those that regularly generate warning messages.
• Contact your invoicing software provider to ensure the necessary updates are implemented in time.
• Use the test environment to ensure that the September go-live does not disrupt your data reporting.

Important: NAV may impose a default penalty in any case where the business fails to correct erroneous data submissions after receiving a formal notice.

Do you have questions about the 2025 NAV Online Invoice changes?

If you’re unsure whether your business is affected by the September 2025 NAV tightening, or if you have technical questions regarding the use of MODIFY vs STORNO, error handling, or how to prevent fines, feel free to contact our tax advisory team. We can help you navigate the changing regulatory environment and ensure your data reporting complies with the new requirements.

Ildikó Hajnal-Balázs

Tax Manager | Accace Hungary

Book a meeting with Ildikó