unable to download nbextensions' javascript and css file

Question

I am trying to install nbextensions to my jupyter notebook. When opening the notebook, I can see the tab for the nbextensions but is is empty. There is a reload button moving but nothing ever shows. I went to command prompt and the following commands were executed successfully:

pip install jupyter_contrib_nbextensions
pip install https://github.com/ipython-contrib/jupyter_contrib_nbextensions/tarball/master
conda install -c conda-forge jupyter_contrib_nbextensions

But when I try to execute

jupyter contrib nbextension install --user

it seems like all extensions validate but when writing them there is a multitude of errors.

[I 09:49:34 InstallContribNbextensionsApp] - Validating: ok
[I 09:49:34 InstallContribNbextensionsApp] Installing jupyter_contrib_nbextensions items to config in C:\Users\sammy\.jupyter
Enabling: jupyter_nbextensions_configurator
- Writing config: C:\Users\sammy\.jupyter
    - Validating...
      jupyter_nbextensions_configurator  ok
Enabling notebook nbextension nbextensions_configurator/config_menu/main...
Traceback (most recent call last):
  File "C:\Users\sammy\Anaconda3\Scripts\jupyter-contrib-script.py", line 5, in <module>
    sys.exit(jupyter_contrib_core.application.main())
  File "C:\Users\sammy\Anaconda3\lib\site-packages\jupyter_core\application.py", line 266, in launch_instance
    return super(JupyterApp, cls).launch_instance(argv=argv, **kwargs)
  File "C:\Users\sammy\Anaconda3\lib\site-packages\traitlets\config\application.py", line 658, in launch_instance
    app.start()
  File "C:\Users\sammy\Anaconda3\lib\site-packages\jupyter_contrib_core\application.py", line 50, in start
    super(JupyterContribApp, self).start()
  File "C:\Users\sammy\Anaconda3\lib\site-packages\jupyter_core\application.py", line 255, in start
    self.subapp.start()
  File "C:\Users\sammy\Anaconda3\lib\site-packages\jupyter_contrib_nbextensions\application.py", line 226, in start
    super(ContribNbextensionsApp, self).start()
  File "C:\Users\sammy\Anaconda3\lib\site-packages\jupyter_core\application.py", line 255, in start
    self.subapp.start()
  File "C:\Users\sammy\Anaconda3\lib\site-packages\jupyter_contrib_nbextensions\application.py", line 175, in start
    toggle_install_config(self._toggle_value, **kwargs)
  File "C:\Users\sammy\Anaconda3\lib\site-packages\jupyter_contrib_nbextensions\install.py", line 103, in toggle_install_config
    configurator_app.start()
  File "C:\Users\sammy\Anaconda3\lib\site-packages\jupyter_nbextensions_configurator\application.py", line 77, in start
    user=self.user, sys_prefix=self.sys_prefix)
  File "C:\Users\sammy\Anaconda3\lib\site-packages\notebook\nbextensions.py", line 351, in _set_nbextension_state
    cm.update(section, {"load_extensions": {require: state}})
  File "C:\Users\sammy\Anaconda3\lib\site-packages\traitlets\config\manager.py", line 85, in update
    data = self.get(section_name)
  File "C:\Users\sammy\Anaconda3\lib\site-packages\traitlets\config\manager.py", line 63, in get
    return json.load(f)
  File "C:\Users\sammy\Anaconda3\lib\json\__init__.py", line 299, in load
    parse_constant=parse_constant, object_pairs_hook=object_pairs_hook, **kw)
  File "C:\Users\sammy\Anaconda3\lib\json\__init__.py", line 354, in loads
    return _default_decoder.decode(s)
  File "C:\Users\sammy\Anaconda3\lib\json\decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "C:\Users\sammy\Anaconda3\lib\json\decoder.py", line 357, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 6 column 22 (char 137)

Any idea where the issue could be? Many thanks!