Unable to progress in milkman level

[bagel801]

I am unable to enter the post office in the milkman level because I can't enter the password into the keypad. No buttons on the keyboard or mouse will allow me to enter the code or even a single number

This kind of problem makes no sense and is usually solved by doing something obvious like resetting the controls, but I've already tried everything I can think of including that. Why can't I enter the code?