Thanks for updating the thread.
When I logged into the website backend, under X > Settings > Permissions necessary selection for Editor role was not there to activate Cornerstone. I have made the changes, please login and see how it goes.
In case changes are not reflecting, please share Editor role login details. As it's a customer website, I don't have the permission to create a new user. To learn more about permissions manager, please take a look at following article: