You’re using the correct template. I’m not sure if OpenOrder can accept “1”, but it can definitely accept “TRUE” and “FALSE”.
If you’re sure that TF Order 039256 - Line 3 exists… I wonder if the DMT is using the wrong plant (site) context. Try logging into Epicor and switching to the site that owns the Transfer Order (MFGSYS). Then log back in to DMT and see if it can find the record.
Be cautious wit TOs the account that is logged into DMT needs to already have the focus of the site that the TO is in, in order to close it.
If you were logged into site A in Epicor doing something, then you logged into DMT to close a TO on site B it would not work. That has been my experience, anyway.