Another note to myself.
In case of

ssh -T user@host

Outputs this type of error.
(Most likely because you forgot to “ssh-add /path_to_your_key”)

Permission denied (publickey).

Delete “config” and “known_host” file from ~/.ssh directory (your default key location)

And if “ssh-add” outputs this error.

Could not open a connection to your authentication agent.

Execute this command

eval “$(ssh-agent)”

Then again. Re-add your key by

ssh-add /path_to_your_key