Add a new ssh user to a droplet

I created a LAMP droplet on ubuntu.

I set it up so I can login on root using SSH, there is no problem there. However I’ve tried multiple tutorials to add a new SSH user and nothing works. I just want a simple way to add an SSH user by using the same SSH key the root user uses. Is there not a tutorial for that?

I’ve created a user (ftphtml), I want ALL the steps to allow that user to login using SSH, could anyone give me the instructions?

I’ve tried this so far:

cp /root/.ssh/authorized_keys /home/ftphtml/.ssh/authorized_keys nano /etc/ssh/sshd_config Added: AllowUsers ftphtml root Uncommented: AuthorizedKeysFile %h/.ssh/authorized_keys service ssh restart

But when I try to login to ftphtml it gives the following error:

Server refused our key