In >2026 to connect to AGOL or Portal enterprise from FME, we utilise the “unified” Esri ArcGIS Enterprise OAuth (Template)(safe.esri-agol) web service ARCGISFEATURESERVICES
Working with Esri ArcGIS Feature Services in FME – FME Support Center
The article perhaps fails to mention how to handle the web service Loopback Interface Redirect or Proxy Redirect Strategy, as the Embedded Browser is deprecated in FME Form 2025.2
The arcgis registered application needs to have http://localhost as redirect URI
What about FME Flow redirect URI?
My suggestion is in Connections & Parameters - FME Flow for any given safe.esri.agol
