# Access to XMLHttpRequest at 'http://api.local/users' from origin 'http://app.local' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

- **ID:** `python/flask-cors-no-access-control-origin`
- **Domain:** python
- **Category:** network_error
- **Verification:** ai_generated
- **Fix Rate:** 80%

## Root Cause

Flask-CORS was not initialized, or the origin was not in the allowed list, so the browser blocked the cross-origin response.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| 4.x | active | — | — |

## Workarounds

1. **** (95% success)
   ```
   from flask_cors import CORS
CORS(app, origins=['http://app.local'], supports_credentials=True)
   ```
2. **** (80% success)
   ```
   @app.route('/users', methods=['GET','OPTIONS'])
def users(): ...
   ```

## Dead Ends

- **** — Preflight OPTIONS requests still fail, so POST/PUT never reach the server. (85% fail)
- **** — Browsers reject wildcard origins when credentials are included. (90% fail)