Hi @ag,

Since you have your App with the Client Id and secret set up already, here's how you can apply them in FME Desktop:

1. Go to Tools > FME Options > Web Connections
2. From that page, click on Manage Services... (in the bottom right)
3. Click the + button on the bottom left of that panel and select Create From > Esri ArcGIS Online
4. Give your new web service a name (this can be anything, just make it easy to know what it is). Then set the Client Id and Client Secret inside there. You can leave everything else at their default values. Note: the text boxes for those will be grey and might look like they can't be edited, but they can.

    

   
5. When you're done, click Apply to create the new Web Service.
6. Make sure to select that Web Service when creating a new connection to ArcGIS Online.

For reference, here is a link to our general documentation on creating and managing Web Services within FME Workbench: http://docs.safe.com/fme/2020.0/html/FME_Desktop_Documentation/FME_Workbench/!NamedConnections/options_web_service_connections.htm

For instructions setting this up on FME Server, please see @siennaatsafe's answer here: https://knowledge.safe.com/questions/88927/how-do-i-reliably-connect-fme-server-201819-to-arc.html

@Laura, thanks for the quick help. The connection works.