Hi @lahoucine,
it should work if you mark the send activity with async-before.
However, I see another problem in your example process. I guess that the process in Pool3 doesn’t work as you expect. This process has two message start events with are joined on an inclusive gateway. If one of these messages is received then a process instance is created. The instance doesn’t wait for the other message.
You must model it in a way that you wait for the first and then for the second message.
Best regards,
Philipp