POS System Developer Needed

Hello, I need a developer to complete and stabilize my POS system.

Project stack:
- .NET 8
- WPF (MVVM)
- SQLite database

What I will provide:
- Full source code (zip/repo)
- Sample database with test data
- Current bug list + missing features list
- Build/run steps

What I need completed:
1) Stabilization
- Fix build/runtime issues
- Clean critical bugs in sales, purchase, inventory, supplier flows

2) Feature completion
- Sales workflow (scan/search/add/remove/discount/tax/hold-recall)
- Payments (cash/card/mixed, partial/credit)
- Purchase orders + supplier returns
- Inventory movements/adjustments, lot/serial handling
- User roles/permissions + audit trail
- Receipt/invoice printing

3) Reporting & accounting checks
- Sales/stock/profit/tax reports
- Journal posting consistency for sales/purchases/returns/payments

4) Reliability & delivery
- Backup/restore
- Validation and error handling improvements
- Final release build + deployment guidance
- Short documentation + handover support

Please send quote in this format:
- Milestone breakdown (M1, M2, M3, M4)
- Fixed price per milestone
- Timeline per milestone
- Included and excluded scope
- Post-delivery support terms
- Similar project experience/examples

Important:
- I prefer milestone-based fixed pricing (not only hourly).
- Please include estimated total duration and total cost.