I'm looking for an experienced mobile app developer to create an invoice trading app for Android. The app should facilitate a trading marketplace and include payment processing. User authentication via email and password is also required. Key requirements: - Trading marketplace functionality - Secure payment processing - User authentication (email/password) Ideal skills and experience: - Proven experience in Android app development - Expertise in building secure payment systems - Knowledge of user authentication protocols Please provide examples of similar work and a timeline for completion.