The aim is to lay all 7 pieces into the box the way that only one number remains open on the number grid. There are 36 different possibilities of placing the pieces.

All the pieces fit together perfectly. If the parts force each other, check your bed setting.

If you want more detail for numbers like me, you can use the “change color” option on your slicer for puzzle_base.stl . Color changing should use on 0.8 - 1 mm height. I've added that gcode.

You can print the parts one by one in different colors or all of them in one color. All STL files added.

If you like my design, please write a comment and share your print with everyone :)