If multiple devices are available, you need to specify the name or IP address (you can list all devices with mdt devices).Internally, this is a normal SSH connection using OpenSSH with key-based authentication. So before you can connect to the device shell with MDT or any other SSH tools, you must push a public key to the device’s /home/mendel/.ssh/authorized_keys file. If no such key exists there, the mdt shell command creates it and pushes it (you can also do this manually with mdt genkey and then mdt pushkey). This key created by MDT is PEM-formatted, passwordless, and saved on your host computer at ~/.config/mdt/keys/mdt.key (this key is used only when connecting with mdt shell).
sudo rm -f /home/mendel/.ssh/authorized_keys