Maybe try posting your question in the Steam forum for the game?
Maybe someone here has played this, but I am pretty sure that no one here has posted a question about it.
The one thing I could find is the following:
Troubleshooting the Dumbwaiter
Input Click and Drag / On-Screen UI: Instead of typing numbers directly via your keyboard, ensure you are left-clicking and specifically dragging or clicking the individual dials/numbers directly on the dumbwaiter interface with your cursor.
If I can find out anything else about this, I will let you know.
