Doorbird integration not working

Hello,

I am using a Doorbird D301A which I want to integrate in Home Assistant.
Unfortunately, as soon as I add the montored_conditions (in my case only the doorbell) to my config, the Doorbird integration won’t initialize (“Setup failed for doorbird: Component failed to initialize.”). If I remove it, then it initializes and I can use my relay.
I have granted the API operator permission to the user (Home Assistant adds a http call which I can see in the Doorbird app).
Whenever I try to call the {Home Assistant URL}/api/doorbird/clear/{DoorBird name} URL, I get either “Unauthorized” if the Doorbird integration is running or an Error 500 if it failed to initialize.

Is there something else I have to do besides the things in the documentation? Thanks very much for your help!