Error Unexpected token '<', "<!DOCTYPE "... is not valid JSON #326

Hello everyone,

First of all, thank you very much for your work. I have just installed this app as a Docker version because my previous solution did not work very well.

Now to my problem: I have successfully created an admin account and installed and connected all apps (Zoom, DAV-Calender). Now I wanted to add a new user. However, when creating the account (Register Account button), I get an error message at the top with the following content: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

Can anyone help here?

Best regards and many thanks in advance.

Christian