Notification/Push Alert Debugger

Help me debug notification/push alert issues.

**Platform:** {{PLATFORM}}
**Service:** {{SERVICE}}

**Backend notification code:**
```{{LANGUAGE}}
{{BACKEND_CODE}}
```

**Client-side code:**
```{{CLIENT_LANGUAGE}}
{{CLIENT_CODE}}
```

**Service configuration:**
```
{{SERVICE_CONFIG}}
```

**Error or issue:**
```
{{ERROR}}
```

**Problem description:** {{PROBLEM}}

Please provide:
1. **Token Validation**: Check device/push tokens
2. **Payload Format**: Verify notification payload format
3. **Permission Issues**: Check notification permissions
4. **Service Configuration**: Verify FCM/APNs/etc. setup
5. **Fixed Code**: Corrected notification code
6. **Retry Logic**: Handle delivery failures
7. **Testing Approach**: How to test notifications
8. **Monitoring**: Track notification delivery