I've seen several older threads on this general topic, but none of the solutions I've seen in them have worked for me.
I'm currently testing out the Attachment Viewer configurable app in ArcGIS Online as a replacement for the "classic" Shortlist storymap template. It looks like the app should be perfect for our purposes - an image-focused layout with a map to provide geographic context. However, I can't seem to get the app to work with the test data that I've cobbled together so far. When previewing, I get the "No attachments found" message, and when I open the builder, a small warning box says, "This application requires a layer that supports attachments and has 'supportsQueryAttachments' set to true."
I'm not sure how to directly check the 'supportsQueryAttachments' flag, but the Query Attachments operation seems to be working just fine on the REST service.
The only thing I'm aware of that I'm doing differently from the tutorials and walkthroughs I've found is that the attachments aren't being created using any of Esri's field collection apps. I used the Enable Attachments and Add Attachments tools in ArcGIS Pro to add the image attachments to the layer in an offline file geodatabase before uploading that layer to AGO.
Does anyone have any idea what I'm doing wrong, or how I could try to fix it?
For reference, here is the layer service I'm using: https://services1.arcgis.com/xUx8EjNc6egUPYWh/ArcGIS/rest/services/TAP_Test/FeatureServer/0
The AGO item page for the layer: https://semcog.maps.arcgis.com/home/item.html?id=dccf0576266a4ac2b19c53dbabcbd5bc
The test app: https://semcog.maps.arcgis.com/apps/instant/attachmentviewer/index.html?appid=9b5d26ab4f80430782584f...
And the test map: https://semcog.maps.arcgis.com/home/webmap/viewer.html?webmap=39cb00ff9b654d92b29a6b4cf6d36c21