One of my clients was trying to connect, for the first time, on his brand new server..
Somehow he wasn’t able to connect….

He showed me the following *log/report*…

Status:    Waiting to retry...
Status:    Connecting to 37.XX.XX.XX...
Response:  fzSftp started
Command:   open "[email protected]" 22
Error:     Server unexpectedly closed network connection
Error:     Could not connect to server

and this is the auth.log on the server…

fatal: no matching mac found: client hmac-sha1,hmac-sha1-96,hmac-md5 server [email protected],hmac-sha2-256-$

Solution?
Update the SFTP client – in this case filezilla -.

Readings?
https://forum.filezilla-project.org/viewtopic.php?t=31738
https://en.wikibooks.org/wiki/OpenSSH/Logging