Hello @Corentin.appart.
As I can see, you are using system.util.sendMessage function, wich only works if the Message Handler is configured either on Client / Gateway / Session Event Scripts.
A Message Handler defined in a perspective component must be called with the function system.perspective.sendMessage. This functions only works is the call and the handler are in the same project.
So, in your case, you must move the message handler defined in the component to a message handler defined in Session event scripts.
