Answers for "It is required that your private key files are NOT accessible by others. This private key will be ignored."

Permissions 0664 for '/home/kapua/keys/dev11' are too open.

chmod 600 ~/.ssh/id_rsa

it is required that your private key files are not accessible by others

$ sudo chmod 600 /path/to/my/key.pem

It is required that your private key files are NOT accessible by others. This private key will be ignored.

# if you are using WSL then include sudo before the commands
sudo ssh ...

It is required that your private key files are NOT accessible by others.

chmod 400 /Users/username/.ssh/id_rsa