For any contest published on Facebook, there are usually two links provided - full link & shortened link.
Full link looks like: https://www.facebook.com/Test-1176305399074619/app/515720611858523/
Shortened link looks like: http://wshe.es/NdMMdEQO
The full link only works on desktop whereas the shortened link works fine universally. This is because the application tabs are not directly visible from mobiles devices. So we strongly recommend you to use the shortened link when you share the contest in public.
The shortened link is always located right below the name of your contest, or also on the left hand side of your contest report page.