Pos_Invoicing

Description:
Handle failure scenarios during POS sync including network failures, retry logic, duplicate prevention, and invalid payload handling. Ensure reliable and consistent data sync between POS and server.

Acceptance Criteria:

Sync retry does not create duplicate records (idempotent behavior)
Failed sync entries stored and retried automatically
Network interruption resumes sync correctly
Invalid payload handled with proper error response
Sync status tracked (pending/success/failed)
No data loss or corruption during retry