When a new event is added to a game it will be added to the DEV environment. You you can integrate, extend and test your event in the DEV environment, but will need to publish it to the LIVE environment before it can accept LIVE events.
If you send events to the LIVE environment before the event has been published it will fail event validation with a "schema not defined" error.
If you make changes to an event on DEV you will also need to use the "Push To Live" button to update the event schema in the LIVE environment.
There is a "Push To Live" button for each event in the "Event Management" Tool in your DEV environment.