PHP X-debug in Visual Code using SFTP extension

Question

I have a virtual box instance running a copy of a production server that is running PHP 7.3. I've lately been using Visual code and a SFTP plugin (VS Code SFTP 1.1.1) to open/edit/save files using SSH, which works nicely. I'm now installed X-debug in the local server to do some debugging but I can't make it work with Visual Studio.

I think that the main problem is that since I open remote files, using the SFTP extension, there isn't a local copy that Visual Code can open when getting info from X-debug.

What happens when I start a debug session and reload the website is that Visual Code gives me this error:

Unable to open 'class_db.php': File not found (file:///c:/var/www/mysite.com/private/script/class_db.php).

Of course "c:/var/www/mysite.com" doesn't exist since I open the files remotely.

My launch.json looks partly like this:

{
  "name": "Listen for XDebug 2",
  "type": "php",
  "request": "launch",
  "port": 9000,
  "log":true,
  "pathMappings": {
    "/var/www/mysite.com": "${workspaceRoot}"
  }
},

The path on the server is correct:

/var/www/mysite.com

I don't know if it's possible to get this to work without having the files locally. I was hoping that the mapping (${workspaceRoot}) would loop back to the SFTP files listing so the file would be opened there but that doesn't seem to be happening.

Does anyone got this kind of setup working?