I am sorry that you are receiving this message. When you go to that URL are you logged in as your personal account or as the business? In order to add the application and accept the permissions we do need your personal account to be logged in. You can also try adding the application via the Application Facebook Page here. You can click the three dots on the right side of the page and choose to "Add App to Page."
Let us know if you are able to add the app or if you are still getting an error page.