This is a simple script that can backup a directory of a server to another server with SFTP.

sftp-server-backup.sh

#!/bin/sh
# Put FTP server details here
SERVER="" # server ip/fdqn
USERNAME=""
PASSWORD=""

# local directory containing source backup files
SOURCEFILES="/var/lib/pterodactyl/volumes/"

# temporary tar.gz file path
TARGZFILE="/var/lib/pterodactyl/volumes/volumes.tar.gz"

# remote server directory path in which backup needs to be put in
BACKUPDIRECTORY="/mnt/A/server-backups/node-60/"

# create a tar.gz archive of the source files
tar -czf "$TARGZFILE" -C "$(dirname "$SOURCEFILES")" "$(basename "$SOURCEFILES")"

# login to remote server using lftp
lftp "sftp://$USERNAME:$PASSWORD@$SERVER$BACKUPDIRECTORY" <<EOF

put "$TARGZFILE"

quit
EOF

# remove the temporary tar.gz file
rm "$TARGZFILE"