Facebook “Business” or “Advertising” accounts can’t manage apps. This is an unavoidable Facebook limitation. Only real user accounts are able to create and manage apps.
Please login to Facebook as a personal account to be able to create app. Then setup this app in the plugin. Then you have two options:
1. You can add your personal Facebook account as “Administrator” to your page. Don’t worry, all posts will be made as your “Business” name, not from your personal account. Association of your personal account with that business page won’t be seen by anyone other then you.
2. Logout from Facebook as personal account, login as your Facebook business account, then to to the plugin Facebook settings and authorize the app as business account.