I have create a webmap in ArcGIS Online, that reference a Map Image layer in our Portal. If I access the map from an iOS device, all layers are visible in Map Viewer.
However, if I open the map in the Field Maps App (connected to ArcGIS Online) on the same device - the Portal layers won't load. The error is:
Domain: com.esri.arcgis.runtime.error
Code: 6004
Description: JSON parser invalid start of JSON.
I expect this is because my Portal is behind a firewall, only accessible through an Azure AD Application Proxy. The browser is able to navigate this, but not Field Maps.
I'm also unable to connect Field Maps to my Portal (10.9.1 - so app should be registered automatically) - just gives a generic server connection error.
Is there going to be a way to work around this - are there extra ports or domains that need adding to the proxy?
Unfortunately I can't publish the layers to AGOL, as I need the map image layer, not a tile layer.