The manufacturer certificate with the machine number goes vertically on the frame directly holding the cash box. This way it is visible when you open the coin door and remove the cash box.
See my Thread Bally Mata Hari - Eye of the day as I have a picture of the exact location of that sticker:
https://i1.pinside.com/8/e7/8e78eedf12f0aef2057dcf896487573d5016babf/resized/740/8e78eedf12f0aef2057dcf896487573d5016babf.jpg
Check Matt's thread (Mata Hari dirty girl) and mine as well, for pictures of the various labels and stickers.
Yves