to enable login banners that are displayed before entering a password, edit the following:

vi /etc/issue.net

Add your message however you like to word it and save/close the file:

***************************************************************************
NOTICE TO USERS
 
This computer system is the private property of its owner, whether
individual, corporate or government. It is for authorized use only.
Users (authorized or unauthorized) have no explicit or implicit
expectation of privacy.
 
Any or all uses of this system and all files on this system may be
intercepted, monitored, recorded, copied, audited, inspected, and
disclosed to your employer, to authorized site, government, and law
enforcement personnel, as well as authorized officials of government
agencies, both domestic and foreign.
 
By using this system, the user consents to such interception, monitoring,
recording, copying, auditing, inspection, and disclosure at the discretion
of such personnel or officials. Unauthorized or improper use of this
system may result in civil and criminal penalties and administrative
or disciplinary action, as appropriate. By continuing to use this system
you indicate your awareness of and consent to these terms and
conditions of use. LOG OFF IMMEDIATELY if you do not agree to the
conditions stated in this warning.
 
**************************************************************************** 

Enable banners to be displayed by editing the SSH config file:

vi /etc/ssh/sshd_config

/etc/ssh/sshd_config

Banner /etc/issue.net

Restart the SSH service:

systemctl restart sshd.service

Reboot the server by typing

reboot