NAV Authenticator is a free Android application developed by Nemzeti Adó- és Vámhivatal (National Tax and Customs Administration). This app is designed to provide two-factor identification for even safer electronic tax administration. By generating a code on the user's mobile device or approving a login notification, the app adds an extra layer of security to the web interface of the Online Invoice System.

To use NAV Authenticator, users need a secondary account in the Online Invoice System and meet the following technical requirements: Android 7.0 or higher, an active internet connection, and a camera for scanning QR codes to add users.

The app allows users to perform various operations, including generating control codes without an internet connection, adding and deleting users, setting notification-based identification, and manually entering data if QR code scanning is not possible.

To establish a connection between the application and the Online Invoice System, users must scan the QR code generated by the system or manually enter the 16-digit code. Once the connection is established, users can enable two-factor identification by entering the control code displayed in the app on the web interface.

NAV Authenticator supports English and German languages, which can be switched under the Settings menu.