Hello @ehunziker,
Thanks for updating the thread.
I checked the licence manager and over there I can see that you have updated the URL. Issue is not related with licence. Try to reinstall Cornerstone. You can reinstall Cornerstone by visiting the X menu. Doing so will automatically install Cornerstone for you. If automatic installation is not happening then you can use the link shared in secure note to download latest version of Cornerstone.
If you still have problems kindly get back to us with the result of the steps above and URL/User/Pass of your WordPress dashboard using the Secure Note functionality of the post to follow up the case.
Thank you.