We have a fairly simple GP Service built, and are building the widget in WAB. The tool is a custom python script (not from Model Builder). Basically you click on the map, and the script runs and returns a calculated value (water pressure, in this case).
The GP Service runs correctly, and in ArcMap the pop-up displays the results, which are just a constructed text string configured in an arcpy.AddMessage... statement.
In WAB, the tool appears to be executing correctly, but no results are returned. This is because the Output section has no configuration. The output page is blank when the tool is finished running. All I need to do is hook up that output tab in the GP Widget in WAB to the arcpy.AddMessage value in my script.
Looking at the config_Geoprocessing.json script, I can see the "outputParams" are empty, so I'm just looking for some tips on what needs to go in there to finish this up.