VS Code Remote Workspace Extension doesn't work

Question

I am trying to edit my php files remotely on the ftp server via the visual studio code extension "Remote Workspace". I've installed the plugin and I've created a workspace file including the following json as it is stated on the link: vscode-remote-workspace

{
    "folders": [{
        "uri": "ftp://username:password@mydomain.com:21/public_html/wp-content/plugins/pluginnamehere",
        "name": "turkeytoastmasters.com"
    }]
}

And after the creation of this file, I tried to open the workspace on vs code. On the EXPLORER view, it shows a continuous sliding bar. Nothing changes and no error/notification is shown.

Could you tell me what the problem here is or how I can fix this problem? Thanks.