You should add Message Wait events in automatic role lanes. You can add Message Wait events in user-defined roles but this does not add any information to the process. The engine runs Message Wait events without the user's intervention.
You must connect a Message Wait event to the process flow using an inbound and an outbound transition. An error appears in the Problems View if the inbound or outbound transitions are missing.
You can add an outbound due transition to allow instances to move to the next activity if it does not receive a notification within a specified time period.
If you define multiple Argument Sets, then Message based transitions become available.
If you configure the Message Wait event to allow interruptions then you must not connect it to the process flow. The Message Wait event defines a separate flow.
You can define an Argument Mapping for the Message Wait event to receive information from the process or the application that triggers the Message Wait event.