Cannot add Content Editor

Hi everyone,

I want to add content Editor Accounts to a hosted Website but when I click "
Add content editor" in Project Settings > Members, the overlay shows up for a second but then it goes to this error page:

I tried in incognito mode, with a different browsers and on a different computer - all the same.
Is this a temporary bug in Webflow? Or am I doing something wrong?

“0 of 3 content editor seats are being used.”, so that cannot be the problem.

I have a call tomorrow to introduce the Client to the Webflow Editor. So it’s rather urgent that I can also create the according editor accounts first.

Any Help would be greatly appreciated!