Thanks for writing in!
There might be a issue with the migration that you have done from sub domain to the main domain.
Also i can see the SSL certificate hasn't install correctly.
Please check this article for help regarding migration.
This is for HTTPS
After done this please check again if the problem resolves if you have any error message please send us so that we can have a look.
There is a common validation issue that some people faces, if you want to check.
Hope this helps!