Hi Vince,

If you are writing Cloud Code for ChallengeStartedMessage, then Spark.getData().nextPlayer is expecting one of the incoming parameters to be "nextPlayer". You can find a list of the default ChallengeStartedMessage parameters through our api docs. To fix this, you would need to add an additional parameter called "nextPlayer" in your client code, which may have a reference to another player.

-Pádraig