I need an Android application that lets me build flexible reminder workflows for my retail customers and then fires those reminders through WhatsApp Business and RCS at exactly the moments I define. Think of it as a lightweight marketing-automation engine sitting on a phone: I create or import an approved template, drop in dynamic placeholders (name, invoice total, due date, etc.), choose one or more trigger times, and the app handles the rest with the APIs I will supply. Scope of work • Architecture & scheduling – A background service (WorkManager or similar) must let me stack any number of triggers per customer and guarantee delivery, even if the device reboots or the network is flaky. • Channel integration – Native integration with my WhatsApp Business API endpoint and RCS messaging gateway. The e-mail API is also available, so structure your code so additional channels can be turned on later without rewriting the core logic. • Template engine – Simple in-app editor that pulls my pre-approved templates, exposes placeholders, and validates message length or media rules imposed by WhatsApp/RCS. • Customer & list management – Import via CSV/JSON, tag customers, and attach them to one or more workflows. • Audit & analytics – Small dashboard showing sent, delivered, read, and failed counts per trigger, plus a JSON log export. • UX – Clean, uncluttered screens that follow Material Design. Only the fields and buttons I truly need; no heavyweight drag-and-drop builders. Acceptance criteria 1. I can schedule a workflow with at least three distinct triggers and see each message land in my own WhatsApp/RCS test numbers on time. 2. If I edit the template text or the trigger time, the app reschedules without duplicating old messages. 3. On reinstall or device reboot, all pending triggers persist and still fire. 4. Source code builds on Android Studio (latest stable) with clear README and one-click gradle build. Please outline your preferred tech stack (Kotlin/Java, database choice, third-party libs) and any prior experience you have with WhatsApp Business or RCS messaging so I can move quickly into development.