| Problem | Likely Cause | Solution | |---------|--------------|----------| | 401 Unauthorized | Wrong user/password or missing role | Assign "REST API access" role in WinCC User Administrator. | | 404 Not Found | Wrong endpoint or API version | Check /swagger endpoint; use /api/v1/... as base. | | 403 Forbidden | User lacks tag read/write permission | Grant tag-specific permissions in WinCC. | | Connection refused | REST API not enabled or wrong port | Verify runtime settings and firewall rules. | | Slow response | Large tag list or high-frequency polling | Use bulk read endpoints; reduce polling rate. |
: Send a POST request to the specific tag endpoint with the new value in the request body. If you'd like, I can help you with: The exact JSON body for writing multiple tags at once. The URL structure for specific WinCC versions. How to handle the 402 error if your license is missing. REST interface in WinCC (RT Professional) wincc rest api
