To insert your present you have to add a pause to your print just before it closes the gap.
I did this for the included gcode file (with a pause to insert your money) so you could use this file to print the Money Lock
This design is made for a neatly folded € 20 bill (Internal gap is : with 66 mm and height 36 + 3 mm
The author marked this model as their own original creation.