This is my third question about posting on Facebook.
Although this may be a duplicate of Mac OS X Facebook login failed - no stored remote_app_id for app but I decid
All developers of a particular app, should be known to Facebook. While the application is in Sandbox mode (i.e. developer only access), all every user who want to use the Facebook platform, for testing/developing the application, will have to be added as a developer.
To know your Facebook ID: findmyfacebookid.com