I just added a layer (from an excel file) to a web map.This map already has 2 other layers. It looks fine in the web map.
When I attempt to make a web map app, from this map, my newest layer of data will not show up. Any advice?
How did you add the Excel file to ArcGIS Online? Was it by dragging and dropping it onto the webmap? If so, that type of layer has limited functionality and the web app could be expecting a fully fledged Hosted Feature Layer - to convert your Excel file (ArcGIS Online likes CSVs), there are instructions here: Publish hosted feature layers—ArcGIS Online Help | ArcGIS
Once it's published, add it into your web map and see if the web app recognises it.
If it doesn't there could be another cause, in that case, what web app are you using?
Retrieving data ...