Before you can login with SFTP, you need to activate SFTP or SSH access in your One.com control panel.

1. Open Cyberduck
2. Click Open Connection
3. Select SFTP (SSH File Transfer Protocol) in the dropdown menu
4. Enter the address of the server in the field Server.
   
   (sftp.one-example.com - make sure to enter sftp to connect securely via SFTP.)
   
   
5. Enter the port number.
   
   (port 22 for SFTP)
   
   
6. Make sure Anonymous Login is not selected.
7. Enter your username
   
   (one-example.com - keep it lowercase and without "www.")
   
   
8. Enter your password
   
   (the one you chose for SSH in your Control Panel)
   
   
9. Click on Connect to connect to the server.
10. Click Allow when you get a warning about an unknown host key.

Note: Remember to replace one-example.com with your own domain.