Mobile Image-PDF Converter

I want a clean, intuitive mobile app (iOS and Android) that lets users turn one or more photos into a single PDF while showing them a live “before vs after” file-size comparison. Each conversion spends coins. Coins can be bought through standard in-app purchases and can also be earned automatically when a user’s personal referral link brings in a new installer; there is no earn-by-usage mechanic.

Because I have no artwork or wireframes yet, the full UI/UX still needs to be designed—from the first onboarding screen to the purchase flow. Once the look and feel are approved, the same team should build the production-ready app, integrate Apple/Google payment gateways for coin packs, and implement a secure backend that tracks balances and referral bonuses in real time.

Deliverables
• Figma (or similar) design files and clickable prototype
• iOS & Android builds ready for App Store / Google Play submission
• Source code with clear setup docs and API keys abstracted
• Short admin guide showing how to change coin prices, referral percentages, and size-comparison thresholds

Acceptance criteria
• Image-to-PDF conversion works offline; size difference is shown instantly before saving or sharing
• Successful purchase instantly credits coins; failed purchase never deducts coins
• Referral link installs trigger coin reward only once per new user/device
• App passes App Store & Google Play review using production payment SDKs

Preferred tech is up to you—native Swift/Kotlin or cross-platform (Flutter, React Native) as long as performance on large image batches stays smooth. Let me know which you recommend and why, plus a realistic timeline to hit the deliverables above.