Privacy policy

Effective date: 3 November 2025

This Privacy Policy explains how MATHCODE d.o.o. (“we”, “us”, “our”) collects, uses and protects your information when you use the BillZi mobile application on Android and iOS (the “App”).

By using BillZi, you agree to the collection and use of information in accordance with this Policy.

1. Data controller and contact

Data controller:
MATHCODE d.o.o.
Croatia

Contact email for privacy matters:
📧 aron@mathcode.hr

2. Scope

This Policy applies to:

  • The BillZi app on Google Play (Android) and Apple App Store (iOS).
  • Any related services we provide through the app.

3. Information we collect

We collect the following categories of information:

3.1 Account and authentication information

  • Account details (e.g. email address, username and other registration data you provide).
  • Authentication information when you sign in with:
    • Google Sign-In
    • Apple Sign-In

We do not store your Google or Apple password; we only receive the data necessary to identify you and create or log into your BillZi account.

3.2 Photos and documents

  • Photos and images you upload or capture in the app.
  • Invoice-related documents and content you manage through BillZi.

These are stored on our servers to provide the core functionalities of the app (e.g. storing and managing invoices).

3.3 Device and usage data

We may collect certain technical and usage information, such as:

  • Device type and model, operating system version, language settings.
  • App version and settings.
  • Usage data (e.g. screens viewed, features used, in-app actions).
  • IP address and similar technical identifiers.

Some of this information may be collected via Firebase Analytics.

3.4 Crash and performance data

We use Firebase Crashlytics and similar tools to collect crash reports and performance data, which can include:

  • Device model, OS version.
  • App version.
  • Technical details about the crash or error.

This data is used only to debug and improve app stability.

3.5 Financial and invoice data

Within the app, you may create and manage invoices and related financial information (e.g. client details, invoice amounts, dates, items).

  • This data is stored on our servers to provide the core invoicing features.
  • We do not store your payment card details (if any payment is processed, it is done through external payment providers or platforms such as Google/Apple, according to their own privacy policies).

4. How we use your information

We use the information described above to:

  1. Provide and operate the app
    • Create and manage your BillZi account.
    • Store and manage your invoices and related documents.
    • Ensure the app functions correctly on your device.
  2. Improve and optimize the app
    • Analyze usage to understand which features are used most.
    • Fix bugs and improve performance using crash and analytics data.
  3. Send push notifications
    • Reminder notifications related to invoices or app usage.
    • You can control push notifications through your device settings.

We do not use your data for advertising or profiling for ads.

5. Legal bases for processing

Depending on your location and applicable laws, we process your personal data on the following bases:

  • Performance of a contract: to provide you with the core functionality of BillZi (e.g. managing invoices, storing your data).
  • Legitimate interests: to maintain and improve the app (e.g. analytics, crash reporting, preventing misuse).
  • Consent: where required, for example for push notifications or certain analytics settings, you may be asked for consent, which you can withdraw at any time via device or app settings (where applicable).

6. Data storage and retention

  • We store your data for as long as your account is active and you use the app.
  • If you request deletion of your account or data, we will delete or anonymize your personal data, except where we are required by law to keep it for longer (for example, certain accounting or tax-related records).

7. Data sharing and third parties

We do not sell your personal data and we do not share it with third parties for their own marketing or advertising purposes.

We may share your data only with:

  1. Service providers (processors)
    These help us operate the app and process data on our behalf:
    • Our custom servers / hosting provider where your invoices and account data are stored.
    • Firebase Analytics (Google) for anonymized/aggregated usage analytics.
    • Firebase Crashlytics for crash reporting.
  2. Authentication providers
    • Google and Apple for social login, when you choose to sign in with those providers.

These service providers process data only according to our instructions and only for the purposes described in this Policy.

8. International data transfers

Some of our service providers (such as Google’s Firebase) may process data on servers located outside your country, including outside the European Economic Area (EEA).

Where such transfers occur, we take reasonable steps to ensure that your personal data is protected in accordance with applicable data protection laws (for example through contractual safeguards).

9. Security

We take appropriate technical and organizational measures to protect your data, including:

  • HTTPS for data transmission.
  • Encrypted storage for sensitive data where appropriate.
  • No passwords stored in plain text (e.g. password hashing where relevant).
  • Access controls and security practices to protect our servers.

However, no system can be completely secure, and we cannot guarantee absolute security of your data.

10. Your rights

Depending on your local laws, you may have some or all of the following rights regarding your personal data:

  • Right of access – to know what data we hold about you.
  • Right to rectification – to correct inaccurate or incomplete data.
  • Right to erasure – to request deletion of your data, subject to legal retention requirements.
  • Right to restriction of processing – to request we limit how we use your data.
  • Right to data portability – to receive your data in a structured, commonly used, machine-readable format where technically feasible.
  • Right to object – to object to certain types of processing (for example, analytics based on legitimate interest, where applicable).

To exercise any of these rights, please contact us at: aron@mathcode.hr

You may also have the right to lodge a complaint with your local data protection authority.

11. Children’s privacy

BillZi is not aimed at children and is not intended for use by persons under the age required by applicable law (such as 13 or 16).
We do not knowingly collect personal data from children. If you believe a child has provided us with personal data, please contact us so we can delete it.

12. Changes to this Privacy Policy

We may update this Privacy Policy from time to time. When we do, we will:

  • Update the “Effective date” at the top of this Policy, and
  • Make the updated Policy available in the app and/or on our website.

Your continued use of BillZi after the updated Policy becomes effective means you accept the changes.

13. Contact

If you have any questions or requests regarding this Privacy Policy or your personal data, please contact:

MATHCODE d.o.o.
📧 aron@mathcode.hr

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