From September 2025 (instead of the previously planned date of 1 July), the Hungarian tax authority (NAV) will tighten business validation rules in the online invoice data reporting system. The key change is that 21 current WARNING messages will be reclassified as ERROR messages, resulting in failed data reporting. This aims to improve data integrity, –i.e., the accuracy and reliability of the reported data –, to standardise invoicing practices and to lay the groundwork for the upcoming e-VAT system.
The role of data accuracy and standardisation in successful reporting
NAV’s primary goal is to further improve the quality of online invoice data reporting. The stricter validations will help identify and filter out inaccurate, conflicting, or ambiguous data more effectively. This is in the interest of both the Hungarian tax authority and businesses. Inaccurate data reporting can result in serious risks, including data loss, incorrect VAT returns, penalties, or even audits.
21 WARNING messages will now cause failed data reporting
These 21 reclassified messages mean that any of them will block submission starting September, leading to a failed data reporting. The most common messages being reclassified include (with their respective codes from the NAV REST API specification):
- Tax number errors: when a VAT group member is reported instead of the group itself (codes: 82, 91)
- VAT status issues: incorrect markings like EUFADE, EUFAD37, KBAET, KBAUK (codes: 581–584)
- Exchange rate errors: mismatches between HUF and foreign currency, or extreme rates (codes: 1300–1310)
- Modification document errors: unrealistic or incorrect sequence numbers; original invoice already cancelled (codes: 560, 1140, 1150)
- Tax exemption and performance date inconsistencies (codes include: 591, 593, 596, 330)
New WARNING validation introduced
A new WARNING message will also be introduced to flag incorrect VAT status reporting. It triggers when customerVatStatus = OTHER but the communityVatNumber or thirdStateTaxId starts with “HU” and contains a valid Hungarian VAT number – or when customerTaxNumber/taxpayerId is a valid Hungarian VAT number.
In other words, the system will warn us when a transaction is reported as intra-community or third-country supply, but in fact a Hungarian Community VAT number is indicated for the buyer as a taxable person. Such a discrepancy may lead to more serious consequences later on; therefore, the purpose of the warning is to identify and flag it in time. Unlike the other VAT status issues and incorrect markings mentioned above, this new validation – issued as a WARNING message – doesn’t yet lead to a failed data reporting.
How to avoid failed data reporting for accountants, CFOs or executives
- Review past WARNING messages linked to your invoices.
- Identify which of these will become ERRORs from September.
- Update your processes and systems and perform test runs in the NAV environment.
- Double-check buyer VAT numbers, statuses, and currency exchange data.
What should developers do?
- Review the latest NAV REST API specifications.
- Update your invoicing system’s validation logic according to the new ERROR/WARNING rules.
- Run comprehensive tests in NAV’s sandbox environment.
The NAV’s message with the September 2025 update is clear: data quality is a top priority. While failed data reporting pose real operational and tax risks, the online invoice system has become a key platform for digital taxation in Hungary, not just a compliance tool. Those who adapt early will benefit from smoother cooperation with NAV, those who delay may face serious setbacks.
Source: WTS Klient
For more information, please visit: UPDATED: Failed data reporting in the Hungarian online invoice system
