Error creating an app workspace

Hi, 

I can see that there has been created several posts on this topic already. However, when I try to create an app workspace I get the status code 400, which seems to be different from those reported earlier. Is the issue still the same? 

In the error message I get that I have the wrong prefix or suffix. I then get the following technical details: 

All feedback is highly appreciated!

Kind regards, 

Jonas