NodeRED - unable to install modules

Hello,
I’m quite new to Hass io in general but made my way for some time by googling it. Some days ago I wanted to start using NodeRED but I can’t find a way to install other modules.
Specifically I wanted to install the node-red-contrib-chatbot module but all the time I’ll end up with this error and a pop-up saying the installation failed.

I’ve already tried restarting both, HomeAssistant and NodeRED, tried to update everything (there were updates for both) but neither of them did help…

I also found this thread but it didn’t help me too.

In case it’s something obvious I want to apologise but I just can’t work it out myself somehow…

Thank you very much for your help already,
Toni