I have created a flow action to launch in a modal window.  I have a validation rule for the flow action.  I also create a  temp page with a preprocessing activity.  For example, I am trying to validate that date B takes place after date A.  If it the validation fails, an error would display stating "Date B cannot take place before Date A."   I get an error, but it only shows up on the temp page I created on the clipboard, not in the displayerrors section I added for my modal (per numerous other post recommendations).   How can I get my errors on the temp page I created in my preprocessing activity to appear on the modal and not allow the user to submit the modal until it can pass the validation set forth?

***Edited by Moderator Marissa to update Content Type from Discussion to Question; change General to Product, update Platform Capability tags***