The URL scheme allows for inviting friends to join your game by sending the URL to them or posting it to facebook and twitter.

Undisclosed The URL scheme is undisclosed by the publisher of the application. You are encouraged to contact the publisher for more information.
Application homepage:
iTunes link:
HTML Link example:
Native application URL string example:
Extended example:

This is a undisclosed URL scheme, there should be no need for users to manually create a URL.