Users may see error 'Failed to send request' while login to data loader

Users may see error 'Failed to send request' while login to data loader.

This may be resolved by updating Data Loader Settings and working in conjunction with your network administrator.

Few check that can help to fix:
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1. Check the server host
2. Check your instance
3. Check if you network is using a proxy
4. Check network connectivity
5. Check the port availability

 

More details you can find in the article:  Click here