Cross-platform Ice Sales Tracking App

I need a straightforward mobile app that runs smoothly on both iOS and Android. Its core job is to let me record every ice sale in seconds:

• I select (or add) a customer and their pre-saved price per 1 kg, 3 kg, and 5 kg bag auto-fills.
• I type the quantities sold and the app instantly shows the line total and the grand total.
• At any moment I can open a dashboard that sums all sales: one view groups them by day, another rolls them up by calendar month.

A small back-office screen must let me:
– create, edit, or deactivate customers and their individual price lists;
– correct any mistaken sale;
– back up or export the raw table (CSV or similar).

I’m open to your suggestion on the underlying data store—MySQL, SQLite, Firebase, or another option—so long as it is reliable, lightweight, and gives me an easy path to cloud backup. Please outline why you recommend it.

Deliverables
1. Source code for a single codebase compiling to iOS and Android.
2. Simple, clean UI with the flows above fully working.
3. Database schema and brief setup notes.
4. Installation file(s) and one short video or PDF walk-through showing the key screens in action.

I will shortlist proposals that describe the technical stack, timeline with clear milestones, and any past projects that prove you can ship a solid, cross-platform data-entry app.