tago Thanks for your reply! Now I understand what you are trying to achieve.
To begin with, if you want to roll back your json data from 4.1 to 3.8, you do not need to use Skeleton Viewer. It can be done in the Spine editor.
First, run Spine 4.1 and import the skeleton data you want to roll back. Open the export window and change the Version option in the JSON format options from 4.1 to 3.8. Then run the export to roll back the skeleton data to a format that can be opened in 3.8.
