Negative / Unhappy Path Story Generator

I have a user story focused on the happy path. Help me generate the unhappy path stories and scenarios.

HAPPY PATH STORY:
[The existing user story and its acceptance criteria]

SYSTEM CONTEXT:
- Platforms: [iOS (Swift/SwiftUI) / Android (Kotlin/Compose) / Both]
- Authentication: [How the user is authenticated]
- Network dependency: [Does this require internet? APIs?]
- Data dependencies: [What data must exist for this to work?]

Generate unhappy path scenarios for:
1. Network failures (offline, timeout, partial load)
2. Authentication/authorization failures
3. Invalid input (wrong format, too long, special characters)
4. Missing data (required fields empty, referenced data deleted)
5. Concurrency issues (another user modified the data)
6. Rate limiting or quota exceeded
7. System errors (500s, service unavailable)

For each scenario, provide:
- Given/When/Then acceptance criteria
- Expected user-facing behavior (error message, retry option, fallback)