A Formal Challenge is to be used only when the following steps have been taken without success:

First, attempt to get the game in the lobby

Second, send an email to the player you wish to challenge

Third, if the first two steps are not successful, then use the Formal Challenge as a last resort

Formal Challenges have priority over all other games. If you have a Formal Challenge and both parties are online then you must finish the current game that you are in and play the Formal Challenge