If you cannot login (authenticate) to your server, you generally need to talk to your server administrator. We won’t be able to help you here, unless you can authenticate with other client using the same protocol.
Though check the following articles, as they cover common mistakes and issues:
- “Access denied” error message;
- “Server refused our key” error message;
- Other common error messages;
- Where do I get a username and password?
If you are connecting to your own cloud server, check also guides to connecting to various common cloud platforms (e.g. Amazon AWS, Google Compute Engine, Microsoft Azure, DigitalOcean, etc).