Unable to SSH via key

I am able to log in via console access, but would prefer to use XShell / Putty, but have not been able to login using a key.

Via console access, I can see that the key in ~/.ssh/authorized_keys is identical to the one on my local box (character for character, plus. I can also see that the fingerprints are identical). Yet, I get this error from XShell:

“The selected user key is not registered in the remote host. Try again.”

When I try with Putty (obviously with a correct key), I get this error:

“Disconnected: No supported authentication methods available (server sent: publickey)”

I’ve lost count of how many official DO tutorials I’ve gone through. I’ve also tried speaking with customer support on two separate tickets and it’s been an incredibly frustrating experience as each time I reply, I get a reply from a completely different tech, and not one of them has actually read my ticket fully.

Clearly, I have done something wrong, I just don’t know how to determine what that is. I would be most grateful for any advice on how I can debug this further please. I am leaning heavily towards moving to DO, but at this point am having to consider Vultr as I’ve already wasted a week just trying to figure out how to SSH in to my own server. :/

Thank you very much