Installed and tried to use Fusion 360 Add On. For some reason, I received an error 401 saying that the upload was unsuccessful. The problem would come and go. Finally I discovered that the problem would occur when I was logged on the SimScale Web site when I fired off the Add On.
Please check in the SimScale workbench that the CAD model was actually uploaded.
The message could be misleading and the source of it is being investigated!