Six years ago I released a small Android billing application; today all I have left is the signed APK. The original source code is gone, so I need a developer who can either clean-decompile the APK or, if that proves impractical, rebuild the project from scratch in the latest Android Studio while matching the existing workflow. Core workflow to preserve – billing and invoicing, – customer management, and – reporting and analytics. On top of that I want to add inventory management and a secure user-authentication layer. I have not fixed a login method yet, so you are free to recommend email/password, biometric, social sign-in or any modern alternative that fits the current Google Play guidelines. I will provide the live APK and a short screen-capture showing how it is used inside my business so you can understand the logic, layouts and data flow. Your job is to reproduce that functionality, modernise the UI with Material components, ensure the codebase is future-proof (Kotlin preferred, Java acceptable), and deliver a build that runs smoothly from Android 8 through Android 14. Deliverables • Complete Android Studio project with clean, well-commented code • Working debug APK and release-signed AAB ready for Google Play • Integrated modules for the five features listed above • Basic documentation explaining project structure, libraries, build steps and how to maintain or extend it I’ll be quick to answer questions and can test builds daily, so we can iterate fast. Let me know how you would approach recovering the logic from the APK, which tools you usually use for reverse engineering or rebuilding (Jadx, Apktool, etc.), and a rough timeline to reach first runnable build.