Hey there! It's not listed, but to stamp packages, you can either right click or press R. The devs are currently working to make the game more understandable in future updates, so sit tight! Have a good day!
So I have heard about this weighing machine bug that has been occurring. The weighing machine will bug out and display money instead of actual scale, and when a stamp is placed, the scale will display ERROR. I have managed to track it down, and it seems like leaving a package overnight on the scale will bug it. I have tried it with another save file, and it still worked. Let me know if it works for you.
