Running InAppLocalhostServer from AppDocumentDirectory not working

Question

I'm trying to run the InAppLocalhostServer with files stored in the AppDocumentDirectory but I only get a white screen. When trying with the same files from the asset folder it works perfectly.
Is there any way I can do this from the AppDocumentDirectory?

I tried to address it with file:// or just a leading /, nothing did work.

That's my code:

localhostServer = InAppLocalhostServer(
      documentRoot:
          '/data/user/0/com.my.testapp/app_flutter/www/',
    );
    await localhostServer.start();

And in the WebView:

initialUrlRequest: URLRequest(
    url: WebUri('http://localhost:8080/index.html'),