ssh account for upload files only (SSH)

SFTP Setup:
/etc/ssh/sshd_config:

    Subsystem sftp internal-sftp
    Match Group sftpusers
    PasswordAuthentication yes
    ChrootDirectory /srv/sftponly
    AllowTCPForwarding no
    X11Forwarding no
    ForceCommand internal-sftp

Adding the sftp group:
    groupadd sftpusers

Creating the only account for SFTP Access
    useradd -d /srv/sftponly -g sftpusers -s /bin/false sftpuser
    passwd sftpuser

Restart openssh:
    /etc/init.d/ssh restart

Setting Permission for the directory
chown root:root /srv ; chown root:root /srv/sftponly ; chmod 755 /srv ; chmod 755 /srv/sftponly

Making a Public Directory:
mkdir /srv/sftponly/public
chown sftpuser:sftpusers /srv/sftponly/public/
chmod 333 /srv/sftponly/public/
ls -ltd
d-wx-wx-wx 2 sftpuser sftpusers 4096 Oct 15 14:51 /srv/sftponly/public/

 ref

https://www.unix.com/unix-for-advanced-and-expert-users/238265-sftp-resticting-only-uploading-file.html

ssh legacy option

some older ssh server only support limited key exchange algorithm.

When you get this error:

no matching key exchange method found. Their offer: diffie-hellman-group-exchange-sha1,diffie-hellman-group1-sha1

Use this option :
-oKexAlgorithms=+diffie-hellman-group1-sha1

eg:

ssh -oKexAlgorithms=+diffie-hellman-group1-sha1 user@legacyhost

or put this in your .ssh/config file:

Host myhost.example.org
 KexAlgorithms +diffie-hellman-group1-sha1

ref: https://www.openssh.com/legacy.html