It takes 7 moves to open, but after the first few successful moves, it becomes apparent how to solve. (For better or worse - but this is a fine intro into puzzle boxes.)
Created from wisps of internet vapor, based on a youtube video that mentioned this kind of puzzle. The person in the video had made a version from Bruce Vinley (homemadepuzzles.co.uk), but the plans on his site were...meant for wood, not in a CAD version, and it wasn't really clear how it worked or the sizing. If you're interested in learning how to create a puzzle in a CAD program, might check out the "Free Plans" on his site.
Assembly can be done after gluing, but you might play with it pre-glue so you can see how the pieces move. (Right and left are the same piece, I left them labeled for clarity.) The 'longer' tail of the Bottom panel is the part sticking out as you insert the panels.
The "inner box" is 40mm x 20mm x 15mm. The exterior is 80mm x 40mm x 50mm.
The tolerances are rather tight. I ended up printing the top/bottom/right/left upright so I could get a more accurate measure in the gaps - when I printed them flat, the layer height made the pieces too thick sometimes. (If you want to print them flat, maybe have a smaller layer height than the quick .3mm that I used.)
My final product didn't require sanding - just the accurate removal of supports.
The only glue you need to apply is Side1 to Side2. I left a couple of the panels in to help match up Side1 and Side2, glued the box, clamped it, then removed the panels. This prevents the panels from getting glued to either side.
Tweaks, if you were looking for something to improve.
If someone wanted to be enterprising, you could probably modify the rails such that they hold the sides in, when you have the top/bottom/right/left in. I wasn't sure about glue vs. not glue of the puzzle vs. puzzlebox genre, so I erred on the side of puzzlebox.
Another upgrade you might consider, is extending the inner box INTO the other side, so that there's a nice groove for a clean fitting.