I am the following Custom URL in the pop up
arcgis-survey123://?itemID=bbcc61a5c2ee49bc9c07de759b02444f
but it does not appear to work on the Map Image Layer I am using to get the fire hydrants I want to be inspected. It just opens a blank web page.
When I view the same map in ArcGIS Field Maps, the pop-up configuration setting (with Custom URL) is not respected.