Offline-First POS System for Restaurant & Bar (Multi-Currency, Cross-Platform)

I run a restaurant and bar in Costa Rica and need a custom Point of Sale (POS) system to replace a glitchy off-the-shelf product and a manual Excel ledger. The two most critical requirements: (1) Offline-first architecture — we get frequent power outages and internet drops, so each device must run locally and keep working with no connection, then sync to a single source of truth when the internet returns (local database + conflict resolution). (2) Multi-currency support for local tokens, USD, and Costa Rican colones, including per-customer account balances/ledger to replace our Excel log. Core features: customizable floor plan (select a table to start an order; add/remove tables, bar seats, and standing areas); order and tab management. The system must run on our existing Windows touchscreen computer AND on Android and Apple tablets, all referencing one backend — so a web-based app or a cross-platform framework like Flutter or React Native is ideal. I'm looking for a solo developer with proven offline-capable app experience (local DB, sync, conflict resolution) and custom ledger/accounting logic. Please share examples of offline-first or POS work you've built. Additional features (reporting, inventory, etc.) will come as later phases, so ability to deliver a lean phase-one and build from there is a big plus.