Not sure how you’re trying to do this… I have released a new version of software this past week for LAN connected devices that eliminates the need for the Mutliplexer SmartApp ( BTW, it is not a script that you run interactively.)
If you’re using an old ThingShield, I plan to release that code tonight.
The new version is much, much simpler to use, especially on the SmartThings side.