Server error handling

Dash Python
7

Is this really working for you inside a flask/dash app?
I thought this would be impossible: Dash with Flask - #2 by nedned
When I try to do the same with an almost empty html page in templates/, only containing:

<!doctype html>
<html>
    <head>
        <title>Error {{name}}</title>
    </head>
    <body>
        <h1>{{name}}</h1>
        <p>{{description}}</p>
        <p>{{code}}</p>
    </body>
</html>

I get Unexpected token < in JSON at position 0
I do not quite understand where to the rendered template gets send. Clearly, dash/flask is expecting json and not html as the error message states. (I also tried to jsonify the rendered page which obviously didn’t work).

However what I’m ultimately still trying to do is to change the content of any div within my dash/flask app when handle_internal_server_error() is called but this seems to be impossible as callbacks can only be called from components of the app and not programmatically.