I've follow this article http://www.sharepointalex.co.uk/index.php/2012/11/enabling-sharepoint-2013-apps/ step by step to enable apps of SharePoint 2013 public facing site and still keep getting
Sorry, apps are turned off. If you know who runs the server, tell them to enable apps.
I viewed the logs the only message that could the issue is
App Management Shared Service Application Proxy is not installed.
below snapshots of settings, what would I missing?
the services
App Management Service / Microsoft SharePoint Foundation Subscription Settings Service are started