No matter how many times you snap it together, it comes apart again as soon as you open it.
Here is how I fix them.
Snap one of the hinges together. Leave the other apart for now.
Drill a hole as shown through both halves of the hinge.
Make it just big enough to pass a small nylon cable tie.
Pass a tie through the hole, around the hinge and secure it.
Now snap the other part of the hinge together. It will be easy since the repaired end will not fall apart.
Drill it and secure it in the same way.
It is that simple!
You can open the toolbox as many times as you want and it will not fall apart again.
I used used white cable ties for clarity. Normally I would use black ones so they don't stand out.