I have followed the steps at https://community.safe.com/s/article/How-to-create-an-FME-Web-Connection-for-Esri-ArcGIS-Portal-Feature-Service-OAuth-2-0?t=1688516897087 for FME Form only.
After I am presented with the authentication challenge and log in with our portal administrator account I receive:
"unable to retrieve access token"
"Request to update access token failed. HTTP Error: HTTP/1.1. 500 Internal Server Error