Your latch can be tightened rather simply. You can place your PlanetBox on a firm surface, and open the latch. Then put your thumbs on either side of the top of the latch, and give it a firm push towards the box (away from you). Test the latch now by opening and closing it to see if it is now tight enough. If not, try again a little harder this time. It requires a small but hard push to move the latch wire ever so slightly, but that’s all that is needed to tighten it up.
Here is short video showing you how: