PS. now I added the VideoLibrary.Sync and the GUI.Notification calls to the end of my transmission-postprocess script (with curl), and it is working. So I ended up having the same effect. But still it puzzles me why the amc script fails.

Hello, On my Synology NAS, I get the HTTP 401 too. Using curl (from the NAS, same user transmission), it's all ok. The end of amc log: Notify Kodi: [host:xxx:[email protected], port:8080] GET: http://xxx:[email protected]:8080/jsonrpc?request=%7B%22jsonrpc%22%3A%222.0%22%2C%22method%22%3A%22GUI ...