x5mR As far as I know, you need to create the path for the log file inside the "plutonium" folder, as you can see in the image: "Plutonium\storage\t5\logs"

You also need to specify within your server configuration file the path of your log, as you can see in the image, that matches the path "logs\yourlogfile.log"

And finally in your IW4MAdmin configuration file, "IW4MAdminSettings.json", in the T5 server configuration section, you must specify the path of your log path manually in "ManualLogPath", as the image shows:

This is how I have my server configured.