Multi-layer duplicate prevention system:
- Enhanced frontend duplicate detection with tracking number, amount, and date comparison
- Added MongoDB compound index to prevent database-level duplicates
- Improved backend error handling for duplicate key violations
- Added cleanup endpoint to remove existing duplicates
- Enhanced user feedback for import operations
Frontend changes:
- Stricter duplicate detection comparing tracking number, vendor, amount, and date
- Better error handling and user feedback for duplicate scenarios
- Added 'Clean Duplicates' button to remove existing duplicates
Backend changes:
- Database compound index on reference, vendor, userId, amount, date
- Enhanced error responses with duplicate detection flags
- New POST /expenses/cleanup-duplicates endpoint
- Improved duplicate key error handling
This should eliminate the double Australia Post expense entries.