ScriptError: Authorization is required to perform that action

Hi.
I’ve installed this add-on and was very much looking forward to trying it out. However, when ever I try to, I get the error “Authorization is required to perform that action”. From the wording, I get the feeling that this is a very simple problem of not having checked a box somewhere - but nonetheless, I have not been able to search my way to a solution.
I’m running G-Suite and I am an admin, and have made the installation for the entire domain.

Any thoughts?

best, Lars