Workflows are working asynchronously as explained here: here: https://docs.mendix.com/refguide/workflow-engine/#31-instantiation
Would you could do to make this work is to direct the user to a form/page that has to be completed -before- the workflow is initiated and from a button or microflow start the workflow (CallWorkflow). Example here: https://docs.mendix.com/refguide/workflow-how-to-configure/#5-triggering-the-workflow-from-a-page