The Copy/Paste functionality of our web console is a bit odd; the code backing it is custom due to the way the VNC window is implemented for accessing your Droplet. It isn’t a good idea, in my experience, to rely on the console for long copy/pasting like an SSH key.
My recommended method to get the key on the Droplet is over SSH itself. You can enable PasswordAuthentication for your Droplet by modifying your /etc/ssh/sshd_config file. Once set to Yes restart the SSH service and connect via an SSH client for a more stable connection. You can then modify your ~/.ssh/authorized_keys file to add the appropriate public key.
Developer Support Engineer II - DigitalOcean
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