Dual-Sided Portable POS Android App

**Android App Development for Dual-Sided Portable POS Terminal (Payconiq + Cash Machine + Compact POS)**

We need an experienced Android developer to build a custom native Android application for a dual-sided portable POS device (similar to the ZCS Z108: Android 14, 8-inch main touchscreen 800x1280 + 2.6-inch secondary customer-facing screen, octa-core, 4GB RAM/32GB ROM, Bluetooth, WiFi, optional 4G, rear camera/barcode scanner support, 58mm thermal printer, NFC optional).

### Core Requirements

1. **Payconiq QR/Barcode Generation (Priority)**
Integrate with the official Payconiq Merchant API (v3) so the merchant can enter an amount on the main screen and instantly display a scannable Payconiq QR code on the secondary customer-facing screen (and/or main screen).
- No need for the merchant to use a personal smartphone.
- Support dynamic QR codes (amount + optional reference/description).
- Handle payment status (pending/success/failed/expired) via API polling or webhooks/callbacks.
- Display clear confirmation on both screens.
- Proper error handling, API key/merchant ID management, and compliance with Payconiq branding guidelines for the QR code.

2. **Cash Machine / Cash Device Integration**
We already have working source code from an existing Android tablet app that communicates with our cash device via **Bluetooth **.
- Port / adapt this communication layer into the new app.
- Support cash payment flow in real time > client can choose to pay cash or payconiq
- Reliable connection management, reconnection, and status feedback.

3. **Barcode Scanning**
Use the device’s built-in rear camera to scan product barcodes (or customer barcodes).
- Fast, reliable scanning with visual/audio feedback.
- Add scanned items to the cart.

4. **Compact POS System**
Build a simple, fast, and clean point-of-sale interface optimized for the dual-screen form factor and portable use:
- Product catalog / quick-sale buttons (categories + searchable items).
- Cart management (add/remove/quantity/discount).
- Multiple payment methods: Payconiq (primary), Cash (triggers cash machine), and placeholder for future methods.
- Receipt printing via the built-in 58mm thermal printer.
- Basic sales history / daily summary. > pushed to a cloud as backup
- Simple settings (merchant credentials, printer, cash drawer, language).
- Optimized UI for both merchant (main 8") and customer (2.6" secondary) screens.
- Offline-tolerant where possible (queue payments when needed).

### Technical Expectations
- Native Android (Kotlin preferred, Dart ,Java acceptable).
- Clean, maintainable architecture (MVVM or similar).
- Proper handling of dual displays.
- Secure storage of API keys and credentials.
- Support for the target hardware (Z108-class devices running Android 14).
- Source code delivery + basic documentation + handover.

### Deliverables
- Fully working APK + full source code on GitHub
- Integration of the existing cash-device communication code.(code available)
- Working Payconiq QR generation and status handling.
- Barcode scanning and basic POS flow.
- Short user/admin guide.

### Preferred Skills
- Strong Android native development experience.
- Previous work with POS / dual-screen devices / payment terminals is a big plus.
- Experience with payment APIs (especially QR-based such as Payconiq, or similar).
- Bluetooth + TCP/IP socket communication.
- Camera / barcode scanning libraries (ML Kit, ZXing, or hardware scanner SDKs).

Please include in your proposal:
- Relevant experience (POS, dual-screen, payment integrations).
- Estimated timeline and fixed price or milestone-based quote.
- Any questions about the existing cash-device source code or Payconiq account access.

We will provide the existing cash-device source code, device access/details, and Payconiq merchant credentials after NDA/signing.

Looking for a reliable developer who can deliver a solid, production-ready solution.