I'm trying to create a new GeoForm app in ArcGIS Online. I have a feature service that's shared with the appropriate groups, and enabled for editing:

and the feature service is enabled for editing:

However, when I try to create a new GeoForm web app using a map (which is also shared with the same groups) that contains this feature service, i get the following error after choosing the web map, when selecting the editable layer:

Why am I getting this error, and what do I need to do to configure my feature service properly? Am I missing something?
Thanks,
Jon.