You'll probably have to verify that the redirect URI specified in the web connection is exactly the same as the one specified in the Autodesk BIM360/ACC console.

Thanks @david_r​ 

I'm getting this error when trying to add a web connection.

Normally, I clicked on add web connection, then on authenticate and I'm supposed to be redirected on a signing page for Autocad Cloud Construction instead of an error message.

I haven't entered anything on the list options parameters so I don't know where to verify redirect URI that you are referring to.

You'll need to look at the web service configuration, not the connection. In FME Workbench, look under:

Tools / FME Options / Web connections / Manage services

See also https://docs.safe.com/fme/html/FME_Desktop_Documentation/FME_Desktop/!NamedConnections/options_web_service_connections.htm#Viewing,