When I try to add the Custom Field group to the Post type, I select the Post type to the custom field group but fields are not visible under the Post type. Can you please help me why the fields are not visible in the Post type?
I can't tell from your screenshots why the field groups are not showing up in the column settings for the post type, I'd need to take a look at your site if that's possible.
Let me mark your next reply as private so that we can get log-in credentials from you—you may want to create a temporary admin user for us to use that you can later delete. And be sure to have a current backup of your site.
If I can't spot the issue by inspecting the set up, it may be necessary to take a copy of the site to install locally for deeper debugging. Would that be okay?