Hi I think there is an error in the post demo link.
Missing a slash / after the tld.
example.itp/..
✔ Your theme is compatible.
Visit the demo post at https://example.itp/83d5c1c9-1c2f-4085-9ce9-e990cf10046e/ to see how your theme looks like in Ghost 2.0
You can also check theme compatibility at https://gscan.ghost.org
However, excellent idea to create a post demo for the compatibility of their theme.
Excellent tool to check the compatibility with your theme.
Successful update without any problem.
Good job, thanks again for Ghost!