The demo app is failing on start with any type of sessions

I have the demo app running, but when I try to start the full avatar session, I get the following error: "Error getting session token: Cannot read properties of null (reading '0')." If I click the "Start Custom Avatar Session", I get the following error: "Error getting session token: Failed to retrieve session token".

Please provide detailed instructions in the README, how to configure the demo to run.