The End block ends the call.
Sometimes there are circumstances in which a call ends naturally, such as if the caller reaches the end of the callflow in an application and there are no paths from the last block. In this case, an End block might seem unnecessary. However, if you want the call to end at a given point, such as in a submodule, you must add an End block to the callflow to ensure the caller is not looped back to the main application.
To add an End block to a callflow, drag and drop the End block onto the end of the callflow.