Hi Steffen,
I saw the message in our logs, unfortunately it doesn’t specify why the token is invalid.
Seeing “Status of you current token: is valid. You can still change it here if you want” doesn’t guarantee that your token has the requested access, it means it is not expired.
As a first step, I suggest to verify that your token has the requested permissions. For that, you can follow the steps documented on this community thread.
If you can’t fetch the list of repositories, then there is something wrong with the token and this is why your Pull Request decoration is not working.