Please try restarting the application and check your Internet connection: the problem might be in it. Remember, in order to play online, you must be currently connected to the Internet.
If there are problems with your connection, please contact your Internet Services Provider ASAP.
NB: There is a known connection issue with Farkle: Live v2.23. On some devices it may lead to losing connection every round. This issue is being worked on and will be fixed with the next update.