My Android project is ready for the next phase and I want an experienced developer to wire in three core services: • User authentication – secure sign-in/sign-up (email, Google, or another trusted provider) • In-app purchases – Google Play Billing v5 with test and production variants fully working • Push notifications – reliable FCM delivery with deep-link routing inside the app The codebase is clean Kotlin with basic screens in place; feel free to refactor where it improves stability or performance. I will hand over the current Git repository along with design assets and expect you to commit incremental changes so I can review progress. Acceptance is straightforward: the APK installs on Android 8-14, each feature above passes a functional test script I’ll supply, and the build is Play-Store-ready with no lint or release blockers. If you have recent experience shipping these exact capabilities and can outline your planned approach (libraries, architecture patterns, test strategy), let’s get started.