Hi @havid0707, triggers can be used to map the data that is provided when starting a new workflow instance to workflow variables. If you programatically start the workflow engine you often don’t need a trigger because your code supplies knows the variableIds that should be used.
but in our product, we have an email trigger. that email trigger will always start new workflow instances providing a value for the emailId key.
in each process, the email trigger maps the 'emailId' key to a variable