Business rule doesnt work as expected on reporting new UISummaryBusiness Rule set up by customer for any requirement on report designer triggers both in Classic and New UI.But the gs.addErrorMessage / gs.addInfoMessage or any custom message does not show Error Message in New UI.As per the development team, this is because the classic UI will refresh the page on Save, which will make the UI message popup.New Report Designer is a single-page app, if you Save it will not reload the entire page, so UI Session messages from a business rule will not be rendered.Report Designer is a Custom UI, implemented in AngularJS, we don't support UI Customization on Custom UI.ReleaseAll supported releases.