Access Plex server with BubbleUpnp?

hi there,
I have my plex music library set on my MCH device and it is accesible through outside network (tested).
Now I want to access it via BubbleUpnp, I set up the server address, port, login credentials and can’t access. It says the credentials don’t work, but I’m completely sure they are correct because they are the same tested on a PC browser…
Do you have any experience with this workflow?
Thanks in advance,