SSH Permission denied (publickey)

I have configured my droplet using the following guide -https://www.digitalocean.com/community/tutorials/initial-server-setup-with-ubuntu-22-04

I then followed this guide to add a GUI - https://www.digitalocean.com/community/questions/how-to-install-graphical-interface

All the steps worked, until the step to establish a secure connection (Step 3 — Connecting to the VNC Desktop Securely).

I ran the code that was provided (changing the user parameter accordingly) -

> ssh -L 59000:localhost:5901 -C -N -l sammy your_server_ip

But I got the following error - Permission denied (publickey).

I do have SSH keys as the authentication method on root, and my non root user can login successfully. So I assume the key was copied successfully to that user.

I was required to set a password for the non root user, and I am not sure if that could be the cause of the error.

How can I fix this error and establish the SSH tunnel?