Using yfiles_jupyter_graphs on custom app

Hello, I am using app example. I wanted to use the yfiles-jupyter-graphs plugin but sadly it gives me this output;

Whenever I try to run the first cell, I get the error: Exception opening new comm.

The first error happened while I try to add extension manager to plugin, I thought it might help.
When I try ‘jupyter-lab’, I can actually see the widget but I can’t see in this scenario.

I also tried doing something like jupyter labextension install yfiles_jupyter_graphs, it said that package is not a valid npm package.