The error message indicates that connection to the FTP server is not established. Any further operations with remote server will fail until reconnection attempt is made.
The error may be caused by connectivity issues such as firewall or antimalware whitelisting. Make sure that local machine can connect to the remote server—no firewall is blocking outgoing connections on the client, and incoming connection at the server.
Double check that your provided username & password, fingerprint, certificate and passphrase is valid and are in supported format. To pinpoint the problem, enable connection debugging option.
See some examples of the Could not connect to FTP server event messages:
- Could not connect to "dc1.local". Authentication failed.
- Could not connect to "dc.lan". Password is set, but Username is not.
- Could not connect to "ec2-10-0-211-96.compute-1.amazonaws.com". Error: Fingerprint for algorithm SHA-256 not supported.
- TLS host certificate fingerprint is not in a correct format.
- Connection failed. Policy requires SSL.
- Server asks for authentication with a client certificate. Policy requires valid SSL Client certificate.
- Peer certificate rejected. Disconnected from server.
- Connection failed. A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond.
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