It's looking for the print service URL, for example: https://webadaptor.domain.com/arcgis/rest/services/Utilities/PrintingTools/GPServer/Export%20Web%20M...
It automatically pulls in the default one set for my ArcGIS Online organization, was there a value in that box when you first created the widget?
Yes this URL show automatically
Try the default ESRI print service: https://utility.arcgisonline.com/arcgis/rest/services/Utilities/PrintingTools/GPServer/Export%20Web%... Otherwise, I would recommend using your own if you have ArcGIS Server